Perception of rotating spiral patterns by pigeons

The ability of pigeons to discriminate indepth moving stimuli was studied with the rotating spiral illusion. Trained with tightly wound spirals, the birds were able to distinguish apparently approaching from apparently retreating spirals. Discrimination also persisted with loosely wound spirals, even though these did not induce an equivalent illusion in humans. Analysis of the optic flow created by the spirals indicates that the relevant cues were local divergent/convergent motion patterns. Global flow patterns, similar to those arising with approaching/retreating scenes, were only generated by tightly wound spirals. An unidimensional parameter could be derived that typified each and all the stimuli used. It is equivalent to the that has been used to characterize the optic flow of really approaching objects, indicating the time to collision. With a stationary rotating logarithmic spiral, is a joint function of winding tightness and rotation velocity. The s associated with the rotation speeds yielding threshold discrimination gauged the effectiveness of spirals with different winding inclinations. Threshold s were high with tight spirals and decreased with loose spirals. This indicates that both local and global kinetic cues must contribute to the detection of in-depth movement by pigeons. Even though the cue efficiency of local flow patterns alone is less than that of global flow patterns the former may be of value when they are dealing with scene elements looming at different rates or with looming objects that are partially occluded.     

Reisolation of Nitrosospira briensis S. Winogradsky and H. Winogradsky 1933

Summary Nitrosospira briensis was isolated from the soils of Crete, the Greek mainland and Switzerland. This is only the second report of the reisolation of a member of this genus since it was described by the Winogradskys in 1933. N. briensis, studied in the present investigation, is so tightly coiled that the cells appear as rods or cylinders rather than spirals when examined with the phase- contrast microscope. On occasion the cells partially uncoil and the spirals are clearly evident even with a phase-contrast microscope. When the cells were thin-sectioned, shadowed, negatively-stained or freeze-etched and viewed with the electron microscope, the spirals were visible even in tightly coiled cells. The tightly coiled cells which appear as rods or cylinders are 1.5–2.5 long and 0.8–1.0 wide. The cells moved erratically and are propelled by 1–6 flagella which were 3–5 long.Contribution No. 2570 from the Woods Hole Oceanographic Institution.     

A serendipic legacy: Erwin Esmarch's isolation of the first photosynthetic bacterium in pure culture

During the 1880's, Erwin von Esmarch was a junior associate (Assistent) of Robert Koch studying bacteria of medical significance. In 1887, he isolated the first example of spiral-shaped bacteria in pure culture, from the dry residue of a dead mouse that he had suspended sometime earlier in Berlin tap-water. Under certain conditions, colonies of the organism were the color of red wine, and this led Esmarch to name the bacterium Spirillum rubrum. Twenty years later, Hans Molisch demonstrated that S. rubrum, an apparent heterotroph, was in fact a non-oxygenic purple photosynthetic bacterium, and it was renamed Rhodospirillum rubrum. Esmarch was a careful investigator and his classic paper of 1887 details the serendipitous isolation and general characteristics of the first pure culture of an anoxyphototroph, which later played a prominent role as an experimental system for study of basic aspects of bacterial photosynthesis. This report includes an English translation of his original paper (in German), a commentary on the historical significance of Esmarch's spirillum, and a summary of Esmarch's career.     

Men in Papua New Guinea Accurately Report Their Circumcision Status

Background

Male circumcision (MC) is a well-established component of HIV prevention in countries with high HIV prevalence and heterosexually driven epidemics. Delivery and monitoring of MC programs are reliant on good quality MC data. Such data are often generated through self-reported MC status surveys. This study examined self-reported MC status in comparison with genital photographs from men in Papua New Guinea (PNG).

Methods

This retrospective non-interventional study collated self-reported MC status data from the ‘acceptability and feasibility of MC’ study at 4 sites in PNG during 2010–2011. Participants reported their MC status based on an 8-category photographic classification covering the range of foreskin cutting practices in PNG. Genital photographs of 222 participants from this study were independently classified by 2 investigators. The 8-category photographic classification was simplified into a 3 category classification of ‘no cut’, ‘straight cut’ and ‘round cut’ before comparing for agreement between self-reporting and investigator assessment using Cohen’s Kappa measure.

Results

Using the 3-category classification, there was 90.6% (201/222) agreement between self-assessment and investigator classification (κ value 0.805). Of the discordant 9.4% (21/222), 3.6% (8/222) self-classified as having a cut foreskin (5 straight cut; 3 round cut) while investigators classified as having no cut; 4.1% (9/222) self-classified as having no cut while investigators classified them as having had a cut (6 straight cut; 3 round cut) and 1.8% (4/222) self-classified as having a round cut while investigators classified as having a straight cut. Given the great variety of foreskin cutting practices and appearances, feasible explanations are suggested for two-thirds (13/21) of these discordant results.

Conclusions

This study demonstrates a high level of agreement between self-reporting and investigator assessment of MC status in PNG and suggests self-reporting of MC status to be highly reliable among men in PNG.     

From discovering to understanding

Friedrich Miescher''s attempts to uncover the function of DNAIt might seem as though the role of DNA as the carrier of genetic information was not realized until the mid-1940s, when Oswald Avery (1877–1955) and colleagues demonstrated that DNA could transform bacteria (Avery et al, 1944). Although these experiments provided direct evidence for the function of DNA, the first ideas that it might have an important role in processes such as cell proliferation, fertilization and the transmission of heritable traits had already been put forward more than half a century earlier. Friedrich Miescher (1844–1895; Fig 1), the Swiss scientist who discovered DNA in 1869 (Miescher, 1869a), developed surprisingly insightful theories to explain its function and how biological molecules could encode information. Although his ideas were incorrect from today''s point of view, his work contains concepts that come tantalizingly close to our current understanding. But Miescher''s career also holds lessons beyond his scientific insights. It is the story of a brilliant scientist well on his way to making one of the most fundamental discoveries in the history of science, who ultimately fell short of his potential because he clung to established theories and failed to follow through with the interpretation of his findings in a new light.…a brilliant scientist well on his way to making one of the most fundamental discoveries in the history of science […] fell short of his potential because he clung to established theories…Open in a separate windowFigure 1Friedrich Miescher (1844–1895) and his wife, Maria Anna Rüsch. © Library of the University of Basel, Switzerland.It is a curious coincidence in the history of genetics that three of the most decisive discoveries in this field occurred within a decade: in 1859, Charles Darwin (1809–1882) published On the Origin of Species by Means of Natural Selection, in which he expounded the mechanism driving the evolution of species; seven years later, Gregor Mendel''s (1822–1884) paper describing the basic laws of inheritance appeared; and in early 1869, Miescher discovered DNA. Yet, although the magnitude of Darwin''s theory was realized almost immediately, and at least Mendel himself seems to have grasped the importance of his work, Miescher is often viewed as oblivious to the significance of his discovery. It would be another 75 years before Oswald Avery, Colin MacLeod (1909–1972) and Maclyn McCarthy (1911–2005) could convincingly show that DNA was the carrier of genetic information, and another decade before James Watson and Francis Crick (1916–2004) unravelled its structure (Watson & Crick, 1953), paving the way to our understanding of how DNA encodes information and how this is translated into proteins. But Miescher already had astonishing insights into the function of DNA.Between 1868 and 1869, Miescher worked at the University of Tübingen in Germany (Figs 2,​,3),3), where he tried to understand the chemical basis of life. A crucial difference in his approach compared with earlier attempts was that he worked with isolated cells—leukocytes that he obtained from pus—and later purified nuclei, rather than whole organs or tissues. The innovative protocols he developed allowed him to investigate the chemical composition of an isolated organelle (Dahm, 2005), which significantly reduced the complexity of his starting material and enabled him to analyse its constituents.Open in a separate windowFigure 2Contemporary view of the town of Tübingen at about the time when Miescher worked there. The medieval castle housing Hoppe-Seyler''s laboratory can be seen atop the hill at the right. © Stadtarchiv Tübingen, Germany.Open in a separate windowFigure 3The former kitchen of Tübingen castle, which formed part of Hoppe-Seyler''s laboratory. It was in this room that Miescher worked during his stay in Tübingen and where he discovered DNA. After his return to Basel, Miescher reminisced how this room with its shadowy, vaulted ceiling and its small, deep-set windows appeared to him like the laboratory of a medieval alchemist. Photograph taken by Paul Sinner, Tübingen, in 1879. © University Library Tübingen.In carefully designed experiments, Miescher discovered DNA—or “Nuclein” as he called it—and showed that it differed from the other classes of biological molecule known at that time (Miescher, 1871a). Most notably, nuclein''s elementary composition with its high phosphorous content convinced him that he had discovered a substance sui generis, that is, of its own kind; a conclusion subsequently confirmed by Miescher''s mentor in Tübingen, the eminent biochemist Felix Hoppe-Seyler (1825–1895; Hoppe-Seyler, 1871; Miescher, 1871a). After his initial analyses, Miescher was convinced that nuclein was an important molecule and suggested in his first publication that it would “merit to be considered equal to the proteins” (Miescher, 1871a).Moreover, Miescher recognized immediately that nuclein could be used to define the nucleus (Miescher, 1870). This was an important realization, as at the time the unequivocal identification of nuclei, and hence their study, was often difficult or even impossible to achieve because their morphology, subcellular localization and staining properties differed between tissues, cell types and states of the cells. Instead, Miescher proposed to base the characterization of nuclei on the presence of this molecule (Miescher, 1870, 1874). Moreover, he held that the nucleus should be defined by properties that are related to its physiological activity, which he believed to be closely linked to nuclein. Miescher had thus made a significant first step towards defining an organelle in terms of its function rather than its appearance.Importantly, his findings also showed that the nucleus is chemically distinct from the cytoplasm at a time when many scientists still assumed that there was nothing unique about this organelle. Miescher thus paved the way for the subsequent realization that cells are subdivided into compartments with distinct molecular composition and functions. On the basis of his observations that nuclein appeared able to separate itself from the “protoplasm” (cytoplasm), Miescher even went so far as to suggest the “possibility that [nuclein can be] distributed in the protoplasm, which could be the precursor for some of the de novo formations of nuclei” (Miescher, 1874). He seemed to anticipate that the nucleus re-forms around the chromosomes after cell division, but unfortunately did not elaborate on under which conditions this might occur. It is therefore impossible to know with certainty to which circumstances he was referring.Miescher thus paved the way for the subsequent realization that cells are subdivided into compartments with distinct molecular composition and functionsIn this context, it is interesting to note that in 1872, Edmund Russow (1841–1897) observed that chromosomes appeared to dissolve in basic solutions. Intriguingly, Miescher had also found that he could precipitate nuclein by using acids and then return it to solution by increasing the pH (Miescher, 1871a). At the time, however, he did not make the link between nuclein and chromatin. This happened around a decade later, in 1881, when Eduard Zacharias (1852–1911) studied the nature of chromosomes by using some of the same methods Miescher had used when characterizing nuclein. Zacharias found that chromosomes, such as nuclein, were resistant to digestion by pepsin solutions and that the chromatin disappeared when he extracted the pepsin-treated cells with dilute alkaline solutions. This led Walther Flemming (1843–1905) to speculate in 1882 that nuclein and chromatin are identical (Mayr, 1982).Alas, Miescher was not convinced. His reluctance to accept these developments was at least partly based on a profound scepticism towards the methods—and hence results—of cytologists and histologists, which, according to Miescher, lacked the precision of chemical approaches as he applied them. The fact that DNA was crucially linked to the function of the nucleus was, however, firmly established in Miescher''s mind and in the following years he tried to obtain additional evidence. He later wrote: “Above all, using a range of suitable plant and animal specimens, I want to prove that Nuclein really specifically belongs to the life of the nucleus” (Miescher, 1876).Although the acidic nature of DNA, its large molecular weight, elementary composition and presence in the nucleus are some of its central properties—all first determined by Miescher—they reveal nothing about its function. Having convinced himself that he had discovered a new type of molecule, Miescher rapidly set out to understand its role in different biological contexts. As a first step, he determined that nuclein occurs in a variety of cell types. Unfortunately, he did not elaborate on the types of tissue or the species his samples were derived from. The only hints as to the specimens he worked with come from letters he wrote to his uncle, the Swiss anatomist Wilhelm His (1831–1904), and his parents; his father, Friedrich Miescher-His (1811–1887), was professor of anatomy in Miescher''s native Basel. In his correspondence, Miescher mentioned other cell types that he had studied for the presence of nuclein, including liver, kidney, yeast cells, erythrocytes and chicken eggs, and hinted at having found nuclein in these as well (Miescher, 1869b; His, 1897). Moreover, Miescher had also planned to look for nuclein in plants, especially in their spores (Miescher, 1869c). This is an intriguing choice given his later fascination with vertebrate germ cells and his speculation on the processes of fertilization and heredity (Miescher, 1871b, 1874).Another clue to the tissues and cell types that Miescher might have examined comes from two papers published by Hoppe-Seyler, who wanted to confirm his student''s results, which he initially viewed with scepticism, before their publication. In the first, another of Hoppe-Seyler''s students, Pal Plósz, reported that nuclein is present in the nucleated erythrocytes of snakes and birds but not in the anuclear erythrocytes of cows (Plósz, 1871). In the second paper, Hoppe-Seyler himself confirmed Miescher''s findings and reported that he had detected nuclein in yeast cells (Hoppe-Seyler, 1871).In an addendum to his 1871 paper, published posthumously, Miescher stated that the apparently ubiquitous presence of nuclein meant that “a new factor has been found for the life of the most basic as well as for the most advanced organisms,” thus opening up a wide range of questions for physiology in general (Miescher, 1870). To argue that Miescher understood that DNA was an essential component of all forms of life is probably an over-interpretation of his words. His statement does, however, clearly show that he believed DNA to be an important factor in the life of a wide range of species.In addition, Miescher looked at tissues under different physiological conditions. He quickly noticed that both nuclein and nuclei were significantly more abundant in proliferating tissues; for instance, he noted that in plants, large amounts of phosphorous are found predominantly in regions of growth and that these parts show the highest densities of nuclei and actively proliferating cells (Miescher, 1871a). Miescher had thus taken the first step towards linking the presence of phosphorous—that is, DNA in this context—to cell proliferation. Some years later, while examining changes in the bodies of salmon as they migrate upstream to their spawning grounds, he noticed that he could, with minimal effort, purify large amounts of pure nuclein from the testes, as they were at the height of cell proliferation in preparation for mating (Miescher, 1874). This provided additional evidence for a link between proliferation and the presence of a high concentration of nuclein.Miescher''s most insightful comments on this issue, however, date from his time in Hoppe-Seyler''s laboratory in Tübingen. He was convinced that histochemical analyses would lead to a much better understanding of certain pathological states than would microscopic studies. He also believed that physiological processes, which at the time were seen as similar, might turn out to be very different if the chemistry were better understood. As early as 1869, the year in which he discovered nuclein, he wrote in a letter to His: “Based on the relative amounts of nuclear substances [DNA], proteins and secondary degradation products, it would be possible to assess the physiological significance of changes with greater accuracy than is feasible now” (Miescher, 1869c).Importantly, Miescher proposed three exemplary processes that might benefit from such analyses: “nutritive progression”, characterized by an increase in the cytoplasmic proteins and the enlargement of the cell; “generative progression”, defined as an increase in “nuclear substances” (nuclein) and as a preliminary phase of cell division in proliferating cells and possibly in tumours; and “regression”, an accumulation of lipids and degenerative products (Miescher, 1869c).When we consider the first two categories, Miescher seems to have understood that an increase in DNA was not only associated with, but also a prerequisite for cell proliferation. Subsequently, cells that are no longer proliferating would increase in size through the synthesis of proteins and hence cytoplasm. Crucially, he believed that chemical analyses of such different states would enable him to obtain a more fundamental insight into the causes underlying these processes. These are astonishingly prescient insights. Sadly, Miescher never followed up on these ideas and, apart from the thoughts expressed in his letter, never published on the topic.…Miescher seems to have understood that an increase in DNA was not only associated with, but also a prerequisite for cell proliferationIt is likely, however, that he had preliminary data supporting these views. Miescher was generally careful to base statements on facts rather than speculation. But, being a perfectionist who published only after extensive verification of his results, he presumably never pursued these studies to such a satisfactory point. It is possible his plans were cut short by leaving Hoppe-Seyler''s laboratory to receive additional training under the supervision of Carl Ludwig (1816–1895) in Leipzig. While there, Miescher turned his attention to matters entirely unrelated to DNA and only resumed his work on nuclein after returning to his native Basel in 1871.Crucially for these subsequent studies of nuclein, Miescher made an important choice: he turned to sperm as his main source of DNA. When analysing the sperm from different species, he noted that the spermatozoa, especially of salmon, have comparatively small tails and thus consist mainly of a nucleus (Miescher, 1874). He immediately grasped that this would greatly facilitate his efforts to isolate DNA at much higher purity (Fig 4). Yet, Miescher also saw beyond the possibility of obtaining pure nuclein from salmon sperm. He realized it also indicated that the nucleus and the nuclein therein might play a crucial role in fertilization and the transmission of heritable traits. In a letter to his colleague Rudolf Boehm (1844–1926) in Würzburg, Miescher wrote: “Ultimately, I expect insights of a more fundamental importance than just for the physiology of sperm” (Miescher, 1871c). It was the beginning of a fascination with the phenomena of fertilization and heredity that would occupy Miescher to the end of his days.Open in a separate windowFigure 4A glass vial containing DNA purified by Friedrich Miescher from salmon sperm. © Alfons Renz, University of Tübingen, Germany.Miescher had entered this field at a critical time. By the middle of the nineteenth century, the old view that cells arise through spontaneous generation had been challenged. Instead, it was widely recognized that cells always arise from other cells (Mayr, 1982). In particular, the development and function of spermatozoa and oocytes, which in the mid-1800s had been shown to be cells, were seen in a new light. Moreover, in 1866, three years before Miescher discovered DNA, Ernst Haeckel (1834–1919) had postulated that the nucleus contained the factors that transmit heritable traits. This proposition from one of the most influential scientists of the time brought the nucleus to the centre of attention for many biologists. Having discovered nuclein as a distinctive molecule present exclusively in this organelle, Miescher realized that he was in an excellent position to make a contribution to this field. Thus, he set about trying to better characterize nuclein with the aim of correlating its chemical properties with the morphology and function of cells, especially of sperm cells.His analyses of the chemical composition of the heads of salmon spermatozoa led Miescher to identify two principal components: in addition to the acidic nuclein, he found an alkaline protein for which he coined the term ‘protamin''; the name is still in use today; protamines are small proteins that replace histones during spermatogenesis. He further determined that these two molecules occur in a “salt-like, not an ether-like [that is, covalent] association” (Miescher, 1874). Following his meticulous analyses of the chemical composition of sperm, he concluded that, “aside from the mentioned substances [protamin and nuclein] nothing is present in significant quantity. As this is crucial for the theory of fertilization, I carry this business out as quantitatively as possible right from the beginning” (Miescher, 1872a). His analyses showed him that the DNA and protamines in sperm occur at constant ratios; a fact that Miescher considered “is certainly of special importance,” without, however, elaborating on what might be this importance. Today, of course, we know that proteins, such as histones and protamines, bind to DNA in defined stoichiometric ratios.Miescher went on to analyse the spermatozoa of carp, frogs (Rana esculenta) and bulls, in which he confirmed the presence of large amounts of nuclein (Miescher, 1874). Importantly, he could show that nuclein is present in only the heads of sperm—the tails being composed largely of lipids and proteins—and that within the head, the nuclein is located in the nucleus (Miescher, 1874; Schmiedeberg & Miescher, 1896). With this discovery, Miescher had not only demonstrated that DNA is a constant component of spermatozoa, but also directed his attention to the sperm heads. On the basis of the observations of other investigators, such as those of Albert von Kölliker (1817–1905) concerning the morphology of spermatozoa in some myriapods and arachnids, Miescher knew that the spermatozoa of some species are aflagellate, that is, lack a tail. This confirmed that the sperm head, and thus the nucleus, was the crucial component. But, the question remained: what in the sperm cells mediated fertilization and the transmission of hereditary traits from one generation to the next?On the basis of his chemical analyses of sperm, Miescher speculated on the existence of molecules that have a crucial part in these processes. In a letter to Boehm, Miescher wrote: “If chemicals do play a role in procreation at all, then the decisive factor is now a known substance” (Miescher, 1872b). But Miescher was unsure as to what might be this substance. He did, however, strongly suspect the combination of nuclein and protamin was the key and that the oocyte might lack a crucial component to be able to develop: “If now the decisive difference between the oocyte and an ordinary cell would be that from the roster of factors, which account for an active arrangement, an element has been removed? For otherwise all proper cellular substances are present in the egg,” he later wrote (Miescher, 1872b).Owing to his inability to detect protamin in the oocyte, Miescher initially favoured this molecule as responsible for fertilization. Later, however, when he failed to detect protamin in the sperm of other species, such as bulls, he changed his mind: “The Nuclein by contrast has proved to be constant [that is, present in the sperm cells of all species Miescher analysed] so far; to it and its associations I will direct my interest from now on” (Miescher, 1872b). Unfortunately, however, although he came tantalizingly close, he never made a clear link between nuclein and heredity.The final section of his 1874 paper on the occurrence and properties of nuclein in the spermatozoa of different vertebrate species is of particular interest because Miescher tried to correlate his chemical findings about nuclein with the physiological role of spermatozoa. He had realized that spermatozoa represented an ideal model system to study the role of DNA because, as he would later put it, “[f]or the actual chemical–biological problems, the great advantage of sperm [cells] is that everything is reduced to the really active substances and that they are caught just at the moment when they exert their greatest physiological function” (Miescher, 1893a). He appreciated that his data were still incomplete, yet wanted to make a first attempt to pull his results together and integrate them into a broader picture to explain fertilization.At the time, Wilhelm Kühne (1837–1900), among others, was putting forward the idea that spermatozoa are the carriers of specific substances that, through their chemical properties, achieve fertilization (Kühne, 1868). Miescher considered his results of the chemical composition of spermatozoa in this context. While critically considering the possibility of a chemical substance explaining fertilization, he stated that: “if we were to assume at all that a single substance, as an enzyme or in any other way, for instance as a chemical impulse, could be the specific cause of fertilization, we would without a doubt first and foremost have to consider Nuclein. Nuclein-bodies were consistently found to be the main components [of spermatozoa]” (Miescher, 1874).With hindsight, these statements seem to suggest that Miescher had identified nuclein as the molecule that mediates fertilization—a crucial assumption to follow up on its role in heredity. Unfortunately, however, Miescher himself was far from convinced that a molecule (or molecules) was responsible for this. There are several reasons for his reluctance, although the influence of his uncle was presumably a crucial factor as it was he who had been instrumental in fostering the young Miescher''s interest in biochemistry and remained a strong influence throughout his life. Indeed, when Miescher came tantalizingly close to uncovering the function of DNA, His''s views proved counterproductive, probably preventing him from interpreting his findings in the context of new results from other scientists at the time. Miescher thus failed to take his studies of nuclein and its function in fertilization and heredity to the next level, which might well have resulted in recognizing DNA as the central molecule in both processes.One specific aspect that diverted Miescher from contemplating the role of nuclein in fertilization was a previous study in which he had erroneously identified the yolk platelets in chicken oocytes as a large number of nuclein-containing granules (Miescher, 1871b). This led him to conclude that the comparatively minimal quantitative contribution of DNA from a spermatozoon to an oocyte, which already contained so much more of the substance, could not have a significant impact on the latter''s physiology. He therefore concluded that, “not in a specific substance can the mystery of fertilization be concealed. […] Not a part, but the whole must act through the cooperation of all its parts” (Miescher, 1874).It is all the more unfortunate that Miescher had identified the yolk platelets in oocytes as nuclein-containing cells because he had realized that the presumed nuclein in these granules differed from the nuclein (that is, DNA) he had isolated previously from other sources, notably by its much higher phosphorous content. But influenced by His''s strong view that these structures were genuine cells, Miescher saw his results in this light. Only several years later, based on results from his contemporaries Flemming and Eduard A. Strasburger (1844–1912) on the morphological properties of nuclei and their behaviour during cell divisions, and Albrecht Kossel''s (1853–1927) discoveries about the composition of DNA (Portugal & Cohen, 1977), did Miescher revise his initial assumption that chicken oocytes contain a large number of nuclein-containing granules. Instead, he finally conceded that the molecules comprising these granules were different from nuclein (Miescher, 1890).Another factor that prevented Miescher from concluding that nuclein was the basis for the transmission of hereditary traits was that he could not conceive of how a single substance might explain the multitude of heritable traits. How, he wondered, could a specific molecule be responsible for the differences between species, races and individuals? Although he granted that “differences in the chemical constitution of these molecules [different types of nuclein] will occur, but only to a limited extent” (Miescher, 1874).And thus, instead of looking to molecules, he—like his uncle His––favoured the idea that the physical movement of the sperm cells or an activation of the oocyte, which he likened to the stimulation of a muscle by neuronal impulses, was responsible for the process of fertilization: “Like the muscle during the activation of its nerve, the oocyte will, when it receives appropriate impulses, become a chemically and physically very different entity” (Miescher, 1874). For nuclein itself, Miescher considered that it might be a source material for other molecules, such as lecithin––one of the few other molecules with a high phosphorous content known at the time (Miescher, 1870, 1871a, 1874). Miescher clearly preferred the idea of nuclein as a repository for material for the cell—mainly phosphorous—rather than as a molecule with a role in encoding information to synthesize such materials. This idea of large molecules being source material for smaller ones was common at the time and was also contemplated for proteins (Miescher, 1870).The entire section of Miescher''s 1874 paper in which he discusses the physiological role of nuclein reads as though he was deliberately trying to assemble evidence against nuclein being the key molecule in fertilization and heredity. This disparaging approach towards the molecule that he himself had discovered might also be explained, at least to some extent, by his pronounced tendency to view his results so critically; tellingly, he published only about 15 papers and lectures in a career spanning nearly three decades.The modern understanding that fertilization is achieved by the fusion of two germ cells only became established in the final quarter of the nineteenth century. Before that time, the almost ubiquitous view was that the sperm cell, through mere contact with the egg, in some way stimulated the oocyte to develop—the physicalist viewpoint. His was a key advocate of this view and firmly rejected the idea that a specific substance might mediate heredity. We can only speculate as to how Miescher would have interpreted his results had he worked in a different intellectual environment at the time, or had he been more independent in the interpretation of his results.We can only speculate as to how Miescher would have interpreted his results had he worked in a different intellectual environment at the time…Miescher''s refusal to accept nuclein as the key to fertilization and heredity is particularly tragic in view of several studies that appeared in the mid-1870s, focusing the attention of scientists on the nuclei. Leopold Auerbach (1828–1897) demonstrated that fertilized eggs contain two nuclei that move towards each other and fuse before the subsequent development of the embryo (Auerbach, 1874). This observation strongly suggested an important role for the nuclei in fertilization. In a subsequent study, Oskar Hertwig (1849–1922) confirmed that the two nuclei—one from the sperm cell and one from the oocyte—fuse before embryogenesis begins. Furthermore, he observed that all nuclei in the embryo derive from this initial nucleus in the zygote (Hertwig, 1876). With this he had established that a single sperm fertilizes the oocyte and that there is a continuous lineage of nuclei from the zygote throughout development. In doing so, he delivered the death blow to the physicalist view of fertilization.By the mid-1880s, Hertwig and Kölliker had already postulated that the crucial component of the nucleus that mediated inheritance was nuclein—an idea that was subsequently accepted by several scientists. Sadly, Miescher remained doubtful until his death in 1895 and thus failed to appreciate the true importance of his discovery. This might have been an overreaction to the claims by others that sperm heads are formed from a homogeneous substance; Miescher had clearly shown that they also contain other molecules, such as proteins. Moreover, Miescher''s erroneous assumption that nuclein occurred only in the outer shell of the sperm head resulted in his failure to realize that stains for chromatin, which stain the centres of the heads, actually label the region where there is nuclein; although he later realized that virtually the entire sperm head is composed of nuclein and associated protein (Miescher, 1892a; Schmiedeberg & Miescher, 1896).Unfortunately, not only Miescher, but the entire scientific community would soon lose faith in DNA as the molecule mediating heredity. Miescher''s work had established DNA as a crucial component of all cells and inspired others to begin exploring its role in heredity, but with the emergence of the tetranucleotide hypothesis at the beginning of the twentieth century, DNA fell from favour and was replaced by proteins as the prime candidates for this function. The tetranucleotide hypothesis—which assumed that DNA was composed of identical subunits, each containing all four bases—prevailed until the late 1940s when Edwin Chargaff (1905–2002) discovered that the different bases in DNA were not present in equimolar amounts (Chargaff et al, 1949, 1951).Unfortunately, not only Miescher, but the entire scientific community would soon lose faith in DNA as the molecule mediating heredityJust a few years before, in 1944, experiments by Avery and colleagues had demonstrated that DNA was sufficient to transform bacteria (Avery et al, 1944). Then in 1952, Al Hershey (1908–1997) and Martha Chase (1927–2003) confirmed these findings by observing that viral DNA—but no protein—enters the bacteria during infection with the T2 bacteriophage and, that this DNA is also present in new viruses produced by infected bacteria (Hershey & Chase, 1952). Finally, in 1953, X-ray images of DNA allowed Watson and Crick to deduce its structure (Watson & Crick, 1953) and thus enable us to understand how DNA works. Importantly, these experiments were made possible by advances in bacteriology and virology, as well as the development of new techniques, such as the radioactive labelling of proteins and nucleic acids, and X-ray crystallography—resources that were beyond the reach of Miescher and his contemporaries.In later years (Fig 5), Miescher''s attention shifted progressively from the role of nuclein in fertilization and heredity to physiological questions, such as those concerning the metabolic changes in the bodies of salmon as they produce massive amounts of germ cells at the expense of muscle tissue. Although he made important and seminal contributions to different areas of physiology, he increasingly neglected to explore his most promising line of research, the function of DNA. Only towards the end of his life did he return to this question and begin to reconsider the issue in a new light, but he achieved no further breakthroughs.Open in a separate windowFigure 5Friedrich Miescher in his later years when he was Professor of Physiology at the University of Basel. In this capacity he also founded the Vesalianum, the University''s Institute for Anatomy and Physiology, which was inaugurated in 1885. This photograph is the frontispiece on the inside cover of a collection of Miescher''s publications and some of his letters, edited and published by his uncle Wilhelm His and colleagues after Miescher''s death. Underneath the picture is Miescher''s signature. © Ralf Dahm.One area, however, where he did propose intriguing hypotheses—although without experimental data to support them—was the molecular underpinnings of heredity. Inspired by Darwin''s work on fertilization in plants, Miescher postulated, for instance, how information might be encoded in biological molecules. He stated that, “the key to sexuality for me lies in stereochemistry,” and expounded his belief that the gemmules of Darwin''s theory of pangenesis were likely to be “numerous asymmetric carbon atoms [present in] organic substances” (Miescher, 1892b), and that sexual reproduction might function to correct mistakes in their “stereometric architecture”. As such, Miescher proposed that hereditary information might be encoded in macromolecules and how mistakes could be corrected, which sounds uncannily as though he had predicted what is now known as the complementation of haploid deficiencies by wild-type alleles. It is particularly tempting to assume that Miescher might have thought this was the case, as Mendel had published his laws of inheritance of recessive characteristics more than 25 years earlier. However, there is no reference to Mendel''s work in the papers, talks or letters that Miescher has left to us.Miescher proposed that hereditary information might be encoded in macromolecules and how mistakes could be corrected…What we do know is that Miescher set out his view of how hereditary information might be stored in macromolecules: “In the enormous protein molecules […] the many asymmetric carbon atoms allow such a colossal number of stereoisomers that all the abundance and diversity of the transmission of hereditary [traits] may find its expression in them, as the words and terms of all languages do in the 24–30 letters of the alphabet. It is therefore completely superfluous to see the sperm cell or oocyte as a repository of countless chemical substances, each of which should be the carrier of a special hereditary trait (de Vries Pangenesis). The protoplasm and the nucleus, that my studies have shown, do not consist of countless chemical substances, but of very few chemical individuals, which, however, perhaps have a very complex chemical structure” (Miescher, 1892b).This is a remarkable passage in Miescher''s writings. The second half of the nineteenth century saw intense speculation about how heritable characteristics are transmitted between the generations. The consensus view assumed the involvement of tiny particles, which were thought to both shape embryonic development and mediate inheritance (Mayr, 1982). Miescher contradicted this view. Instead of a multitude of individual particles, each of which might be responsible for a specific trait (or traits), his results had shown that, for instance, the heads of sperm cells are composed of only very few compounds, chiefly DNA and associated proteins.He elaborated further on his theory of how hereditary information might be stored in large molecules: “Continuity does not only lie in the form, it also lies deeper than the chemical molecule. It lies in the constituent groups of atoms. In this sense I am an adherent of a chemical model of inheritance à outrance [to the utmost]” (Miescher, 1893b). With this statement Miescher firmly rejects any idea of preformation or some morphological continuity transmitted through the germ cells. Instead, he clearly seems to foresee what would only become known much later: the basis of heredity was to be found in the chemical composition of molecules.To explain how this could be achieved, he proposed a model of how information could be encoded in a macromolecule: “If, as is easily possible, a protein molecule comprises 40 asymmetric carbon atoms, there will be 2⁴⁰, that is, approximately a trillion isomerisms [sic]. And this is only one of the possible types of isomerism [not considering other atoms, such as nitrogen]. To achieve the incalculable diversity demanded by the theory of heredity, my theory is better suited than any other. All manner of transitions are conceivable, from the imperceptible to the largest differences” (Miescher, 1893b).Miescher''s ideas about how heritable characteristics might be transmitted and encoded encapsulate several important concepts that have since been proven to be correct. First, he believed that sexual reproduction served to correct mistakes, or mutations as we call them today. Second, he postulated that the transmission of heritable traits occurs through one or a few macromolecules with complex chemical compositions that encode the information, rather than by numerous individual molecules each encoding single traits, as was thought at the time. Third, he foresaw that information is encoded in these molecules through a simple code that results in a staggeringly large number of possible heritable traits and thus explain the diversity of species and individuals observed.Miescher''s ideas about how heritable characteristics might be transmitted and encoded encapsulate several important concepts that have since been proven to be correctIt is a step too far to suggest that Miescher understood what DNA or other macromolecules do, or how hereditary information is stored. He simply could not have done, given the context of his time. His findings and hypotheses that today fit nicely together and often seem to anticipate our modern understanding probably appeared rather disjointed to Miescher and his contemporaries. In his day, too many facts were still in doubt and too many links tenuous. There is always a danger of over-interpreting speculations and hypotheses made a long time ago in today''s light. However, although Miescher himself misinterpreted some of his findings, large parts of his conclusions came astonishingly close to what we now know to be true. Moreover, his work influenced others to pursue their own investigations into DNA and its function (Dahm, 2008). Although DNA research fell out of fashion for several decades after the end of the nineteenth century, the information gleaned by Miescher and his contemporaries formed the foundation for the decisive experiments carried out in the middle of the twentieth century, which unambiguously established the function of DNA.As such, perhaps the most tragic aspect of Miescher''s career was that for most of his life he firmly believed in the physicalist theories of fertilization, as propounded by His and Ludwig among others, and his reluctance to combine the results from his rigorous chemical analyses with the ‘softer'' data generated by cytologists and histologists. Had he made the link between nuclein and chromosomes and accepted its key role in fertilization and heredity, he might have realized that the molecule he had discovered was the key to some of the greatest mysteries of life. As it was, he died with a feeling of a promising career unfulfilled (His, 1897), when, in actual fact, his contributions were to outshine those of most of his contemporaries.…he died with a feeling of a promising career unfulfilled […] when, in actual fact, his contributions were to outshine those of most of his contemporariesIt is tantalizing to speculate the path that Miescher''s investigations—and biology as a whole—might have taken under slightly different circumstances. What would have happened had he followed up on his preliminary results about the role of DNA in different physiological conditions, such as cell proliferation? How would his theories about fertilization and heredity have changed had he not been misled by the mistaken identification of what appeared to him to be a multitude of small nuclei in the oocyte? Or how would he have interpreted his findings concerning nuclein had he not been influenced by the views of his uncle, but also those of the wider scientific establishment?There is a more general lesson in the life and work of Friedrich Miescher that goes beyond his immediate successes and failures. His story is that of a brilliant researcher who developed innovative experimental approaches, chose the right biological systems to address his questions and made ground-breaking discoveries, and who was nonetheless constrained by his intellectual environment and thus prevented from interpreting his findings objectively. It therefore fell to others, who saw his work from a new point of view, to make the crucial inferences and thus establish the function of DNA.? Open in a separate windowRalf Dahm     

Temperature sensitivity of vinblastine-induced tubulin polymerization in the presence of microtubule-associated proteins

The antitumor drug vinblastine has been a useful probe for examining the interaction of tubulin with the microtubule-associated proteins (MAPs), specifically with and MAP 2. Although and MAP 2 can stimulate microtubule assemblyin vitro, their specific interactions with tubulin are known to differ. For example, in the presence of vinblastine, both and MAP 2 cause tubulin to form spirals, but causes formation of clustered spirals of high turbidity, while MAP 2 causes formation of loose spirals of low turbidity [Ludueñaet al., J. Biol. Chem. 259, 12890–12898 (1984)]. Although cold temperatures can inhibit microtubule assembly, cold has no effect on vinblastine-induced tubulin spiral formation. Consequently, we used the vinblastine-tubulin system to examine the interactions of and MAP 2 with tubulin at low temperatures. We found that -tubulin-vinblastine complexes form about as well at 0°C as at 37°C. In contrast, MAP 2-tubulin-vinblastine complexes form much less well at 0°C than at 37°C. We find, however, that MAP 2, at 0°C, will strongly inhibit, and even reverse, formation of the -tubulin-vinblastine complex. This suggests that the temperature-sensitive factor is the MAP 2-stimulated tubulin-tubulin interaction rather than the MAP 2-tubulin interactionper se; this raises the possibility that the tubulin-tubulin interactions stimulated by differ in their temperature sensitivity from those stimulated by MAP 2.     

Teaching cases: Bowel loops and eyelid droops

Abstract: A patient presented with a small-bowel obstruction associated with signs and symptoms of botulism. Fecal cultures were positive for viable Clostridium botulinum. This case emphasizes the importance of a broad differential diagnosis and doing a complete examination to account for all signs and symptoms.The case: A 45-year-old man who was previously healthy presented to the emergency department with acute-onset abdominal distension and mild blurry vision. Despite self-induced vomiting, his abdominal distension worsened. A small-bowel obstruction was diagnosed based on his clinical presentation and the results of radiography (Figure 1). A computed tomography scan of the patient''s abdomen confirmed the obstruction, but did not add any further information. Despite nasogastric suctioning for 12 hours, the patient''s abdomen continued to distend, bowel sounds became diminished and signs of peritonitis (guarding, tenderness) appeared. To avoid bowel perforation, an exploratory laparotomy was performed. No obvious cause of the obstruction was identified.Open in a separate windowFigure 1: Abdominal radiograph obtained while the patient was in an upright position. Note the small-bowel obstruction with multiple air–fluid levels.A neurologist was consulted 5 days later to assess the patient''s worsening neurologic symptoms, including ptosis (Figure 2), diplopia, dysphagia, aphonia and dry mouth. On examination, the patient''s vital signs were normal. Performing the Valsalva manoeuvre did not change his heart rate The patient had bilateral paralysis of cranial nerves 3, 4, 6, 7, 9 and 10. The patient''s pupils were initially dilated but they were sluggishly reactive to light. One day later, his pupils were unreactive to light (Figure 3). Neck flexion was weak, but appendicular strength was preserved. A neurophysiological assessment with repetitive nerve stimulation was performed, which showed an electro-incremental response on high-frequency stimulation, which was suggestive of a presynaptic disorder.Open in a separate windowFigure 2: The patient had ptosis of both eyes.Open in a separate windowFigure 3: Six days after the patient presented with abdominal distension and blurry vision, his pupils became unresponsive to light.Botulism was highly suspected based on the clinical presentation and the neurophysiological findings. Serum, stool and gastric contents were sent for testing. A detailed history revealed no exposure to suspicious foods, and he had no sick contacts. Public health was notified immediately. We administered antitoxin based on his clinical presentation and the the progression of his pupillary symptoms. There was no subsequent progression of his symptoms. The patient''s bowel sounds returned 6 days after the exploratory laparotomy. The patient received nutrition through a nasogastric tube until his neurologic deficits improved. Speech sounds and other deficits gradually improved over several weeks.Initial samples of the patient''s serum, feces and gastric contents as well as food sources were all negative for botulinum neurotoxin and viable Clostridium botulinum. Two fecal samples, taken about 2 and 8 weeks after the onset of symptoms, both tested positive for viable C. botulinum type B. Because the results were positive for C. botulinum type B and negative for toxins, we suspected colonization botulism rather than foodborne botulism. The patient received no further therapy because his symptoms were improving. He remained in hospital with supportive care for 1 month until his dysphagia resolved.Botulism is a rare neuroparalytic illness caused by a neurotoxin produced by C. botulinum. Botulinum neurotoxin causes irreversible inhibition of acetylcholine release, which affects both the autonomic and somatic systems.¹ Although rare, it remains an important public health concern. From 2000 to 2005, there was an average of 5.8 cases of botulism reported each year in Canada.^2–5 A complete review of the patient''s systems and a physical examination, including cranial nerves, will help to establish the diagnosis.⁶There are 4 natural forms of clinical botulism: foodborne, infant, wound and adult intestinal colonization (Open in a separate windowOnce botulism is suspected, the local public health unit and the Botulism Reference Service for Canada should be notified immediately. Samples of the patient''s feces and gastric contents as well as suspect foods should be tested for botulinum neurotoxin and viable C. botulinum. Serum should be tested for botulinum neurotoxin. After appropriate samples are collected, treatment with antitoxin should be considered. Antitoxin against type A, B and E is typically administered. The benefit of this therapy is greatest within the first 24 hours after the onset of symptoms. Respiratory monitoring and support is essential. If flaccid paralysis occurs, it can not be reversed by antitoxin; however, the antitoxin neutralizes circulating toxins and prevents progression of symptoms.     

Thomas huxley: Fossils,persistence, and the argument from design

Conclusion In struggling to free science from theological implications, Huxley let his own philosophical beliefs influence his interpretation of the data. However, he was certainly not unique in this respect. Like the creationists he despised, he made many important contributions to the issue of progression in the fossil record and its relationship to evolutionary theory. Certainly other factors were involved as well. Undoubtedly, just the sheer inertia of ideas played a role. He was committed to a theory of type and was heavily influenced by von Baer, who argued that one could not rate the different types as being higher or lower than the others. By the mid-1850s his animosity toward Owen had become extreme and he tried to discredit the man whenever possible; yet, as I have pointed out, he also was more than willing to cite Owen's early work when it suited his needs.But I believe the crucial factor in Huxley's eventually accepting progression was that he finally disassociated it from the idea of divine plan. This happened gradually through the 1860s and 1870s, as more and more fossil finds provided support for Darwin's theory. In evaluating this new evidence that supported gradualism, Huxley also realized that progression was an intrinsic part of Darwin's theory:The hypothesis of evolution supposes that at any given period in the past we should meet with a state of things more or less similar to the present, but less similar in proportion as we go back in time... if we traced back the animal world and the vegetable world we should find preceding what now exist animals and plants not identical with them, but like them, only increasing their differences as we go back in time, and at the same time becoming simpler and simpler until finally we should arrive at that gelatinous mass which, so far as our present knowledge goes, is the common foundation of all life.In concluding his first lecture to the Americans, he told them: The hypothesis of evolution supposes that in all this vast progression there would be no breach of continuity, no point at which we could say This is a natural process, and This is not a natural process.⁸⁵ Finally for Huxley, progression was no longer linked to Divine Plan.     

Wire marking results in a small but significant reduction in avian mortality at power lines: a BACI designed study

Background

Collision with electric power lines is a conservation problem for many bird species. Although the implementation of flight diverters is rapidly increasing, few well-designed studies supporting the effectiveness of this costly conservation measure have been published.

Methodology/Principal Findings

We provide information on the largest worldwide marking experiment to date, including carcass searches at 35 (15 experimental, 20 control) power lines totalling 72.5 km, at both transmission (220 kV) and distribution (15 kV–45 kV) lines. We found carcasses of 45 species, 19 of conservation concern. Numbers of carcasses found were corrected to account for carcass losses due to removal by scavengers or being overlooked by researchers, resulting in an estimated collision rate of 8.2 collisions per km per month. We observed a small (9.6%) but significant decrease in the number of casualties after line marking compared to before line marking in experimental lines. This was not observed in control lines. We found no influence of either marker size (large vs. small spirals, sample of distribution lines only) or power line type (transmission vs. distribution, sample of large spirals only) on the collision rate when we analyzed all species together. However, great bustard mortality was slightly lower when lines were marked with large spirals and in transmission lines after marking.

Conclusions

Our results confirm the overall effectiveness of wire marking as a way to reduce, but not eliminate, bird collisions with power lines. If raw field data are not corrected by carcass losses due to scavengers and missed observations, findings may be biased. The high cost of this conservation measure suggests a need for more studies to improve its application, including wire marking with non-visual devices. Our findings suggest that different species may respond differently to marking, implying that species-specific patterns should be explored, at least for species of conservation concern.     

Spectral mechanisms of the compound eye in the fireflyPhotinus pyralis (Coleoptera: Lampyridae)

Summary Electroretinograms (ERG) were recorded from dark- and chromatic-adapted compound eyes in the dusk-active firefly,Photinus pyralis , at different wavelengths ranging from 320 to 700 run and over 4.5 log units change in stimulus intensity. ERG waveforms differed in the short (near-UV and violet) and long (yellow) wavelengths (Fig. 1). Waveform differences were quantitated by analysis of rise and fall times as a function of the amplitude of the response. Rise times were found to be relatively constant for all stimulus wavelengths. However, variations in the fall times were detected and followed characteristically different functions for short and long wavelengths (Fig. 2).No significant differences in the slopes of the Vlog-I curves at different stimulus wavelengths were observed (Fig. 3).Spectral sensitivity curves obtained from the ventral sector in dark- and chromatic-adapted conditions revealed peaks in the short ( max 400 nm: Fig. 4; max 430 nm: Fig. 5 A; and max 380 nm; Fig. 5B) and long ( max 570 nm: Figs. 4, 5) wavelengths, suggesting the presence of two spectral mechanisms. The long wavelength (yellow) mechanism was in close tune with the species bioluminescence emission spectrum (Fig. 4B).This investigation was supported in part by NIH Research Grant # EY-00490 (to R.M.C.); Research Grant # 01794N from the Research Foundation of the City University of New York (to A.B.L.); NIGMS Training Grant #1 TO 2 GM 05010-01 MARC (to J.A.H.); and NSF Grant # HES-75-09824 (to C.O.T.). We thank Tom Jensen for technical assistance, Barry Schuttler for his courtesy in allowing us to collect fireflies at his farm, Jean Lall for editorial assistance, and the two anonymous referees whose comments added considerably to the quality of this paper.     

A family caregiver’s relaxation enhances the gastric motility function of the patient: a crossover study

Background

The primary purpose of this study was to assess the effect of a caregiver’s relaxation on the gastric motility function of the patient. The secondary purpose was to evaluate changes in the caregiver’s willingness to perform self-care following feedback on the results of the primary purpose.

Methods

Subjects were 26 patients with a decreased level of consciousness who received gastrostomy tube feeding and their 26 family caregivers. We compared the patient’s gastric motility under the condition of having his or her hand held with and without caregiver relaxation (crossover study). Changes in the caregiver’s willingness to perform self-care following feedback on the results was evaluated using self-administered questionnaires. Hypnosis was used for relaxation. The outcomes assessed for gastric motility function were the motility index and gastric emptying rate by ultrasonography examination.

Results

Hand-holding by the family caregiver while he or she was receiving relaxation enhanced the patient’s gastric motility function. By giving feedback on the results, the caregiver’s willingness to adopt self-care was increased and his or her sense of guilt was reduced.

Conclusions

This study suggested that a caregiver’s relaxation increases the gastric motility function of the patient and that gettinng feedback including the positive results increases the caregiver’s willingness to perform self-care, which consequently reduce the caregiver burden.

     

Hypodipsic-hypernatremia syndrome in an adult with polycythemia: a case report

Background

Hypernatremia is a very common electrolyte disorder and is frequently encountered in out-patient as well as in-hospital settings. We describe an adult who was found to have unexplained relative polycythemia and episodic hypernatremia. A diagnosis of idiopathic hypodipsic-hypernatremia syndrome was made and the patient was managed with a water-drinking schedule.

Case presentation

A 24-year-old South African-Indian man was found to have polycythemia in association with episodes of hypernatremia. Investigations indicated that he had relative polycythemia. He experienced no thirst at a time when his serum sodium concentration was found to be 151?mmol/L. Further testing indicated that his renal response to arginine vasopressin was intact and magnetic resonance imaging of his brain revealed no hypothalamic lesions. A diagnosis of idiopathic hypodipsic-hypernatremia syndrome was made and he was managed with a water-drinking schedule that corrected his hypernatremia.

Conclusion

Hypodipsia should always be considered when a patient without physical or cognitive disability presents with unexplained episodic hypernatremia or with relative polycythemia.

     

The role of calcium in stalk development and in phosphate acquisition in Caulobacter crescentus

Calcium was found to stimulate stalk development in Caulobacter crescentus and to relieve the inhibition of development long known to be caused by phosphate. This suggested that phosphate inhibition could be attributed to its interaction with Ca²⁺, thereby depriving the cells of a factor that promoted development. Calcium was also found to promote phosphate acquisition by the cells, observed as acceleration of growth at extremes of phosphate concentration, as promotion of carbon-source utilization rather than storage, and as support for phosphate-dependent resistance to arsenate inhibition of growth. Cytological studies of dividing cells revealed that stalked siblings had greater access to exogenous phosphate for use in growth or for storage as polyphosphate, and that access of non-stalked sibling to phosphate was dependent on the length of the stalk of the dividing cell. It was concluded that the physiologic role of the stalk is enhancement of phosphate acquisition. The stimulatory role of calcium in this process was attributed to its support of stalk development and to its stabilization of internal membrane/cell envelope association within the cell-stalk juncture.Abbreviations EGTA (ethyleneglycol-bis-(-aminoethyl ether)-N,N-tetraacetic acid) - PHB (poly--hydroxybutyric acid) - Pn (inorganic polyphosphate) This report is dedicated to the memory of an outstanding teacher, Roger Y. Stanier. If he were available to evaluate this work, I could be confident of his providing the most incisive criticism; if not convinced, the reason(s) for his dissatisfaction would be made quite clear, and if convinced, his defense undoubtedly would enlarge my understanding of this microorganism     

Reflections on Ernst Mayr's This is Biology

In this essay I argue that Ernst Mayr's idea that the emergence of evolutionary biology in Western thought was delayed by the pernicious influence of the false ideologies of Platonism, Christianity, and physicalism is ahistorical and anti-evolutionary, that similar ideas, especially his antipathy to physicalism, prejudice his account of the transformation of natural history and medical science into biology, that his organicist resolution of the perennial conflict between mechanism and vitalism is an unstable compound of semi-holism and semi-mechanism, that his conception of biology as the true bridge between the sciences and the humanities, ethics, and social theory is open to question (especially as to the adequacy of the theory of natural selection to account for every aspect of human nature), and that his depiction of science as the sovereign key to understanding everything known to exist or happen in this universe cannot be justified at the bar of reason.     

Dan Salah Tawfik (1955‐2021)—A giant of protein evolution

It was with great sorrow that we have learned of the untimely death of our friend, mentor, collaborator, and hero, Dan Tawfik. Danny was a true legend in the field of protein function and evolution. He had an incredibly creative mind and a breadth of knowledge—his interests spanned chemistry and engineering to genetics and evolution—that allowed him to see connections that the rest of us could not. More importantly, he made solving biochemical mysteries fun: He was passionate about his work, and his face lit up with joy whenever he talked about scientific topics that excited him (of which there were a lot). Conversations with Danny made us all smarter by osmosis.Danny’s own evolution in science began with physical organic chemistry and biochemistry. His PhD at the Weizmann Institute of Science, awarded in 1995, was on catalytic antibodies under the supervision of Zelig Eshhar and Michael Sela. It was followed by a highly productive period at the University of Cambridge’s Centre for Protein Engineering, first as a postdoctoral fellow with Alan Fersht and Tony Kirby, and then as a senior researcher. Among his many achievements during his time in Cambridge was the demonstration that off‐the‐shelf proteins—the serum albumins—could rival the best catalytic antibodies in accelerating the Kemp elimination reaction due to non‐specific medium effects. This work was an early example of unexpected catalytic promiscuity, and it sowed the seed for Danny’s later fascination with “esoteric, niche enzymology” that went far beyond convenient model systems.It was also in Cambridge where Danny first realized the power of the then new field of directed evolution, both for biotechnology and for elucidating evolutionary processes. He and Andrew Griffiths pioneered emulsion‐based in vitro compartmentalization. The idea of controlling biochemical reactions in separate aqueous droplets inspired emulsion PCR and next‐generation sequencing technologies, whereas Danny used it to solve a long‐standing problem in directed evolution; in vitro selection techniques had always been good at identifying ligand‐binding proteins, but compartmentalization finally enabled the directed evolution of ultra‐fast catalysts.Danny returned to Israel in 2001 to join the faculty of the Weizmann Institute of Science where his scientific trajectory further evolved, diverged, and even “drifted”. He developed new methods for enzyme engineering and applied his evolutionary insights into de novo protein design efforts. In this context, Danny’s interest was always focused on how proteins evolve, particularly the connection between promiscuity, conformational diversity, and evolvability. His depth of understanding underpinned both applied research, such as engineering enzymes to detoxify nerve agents, and fundamental research, such as the evolution of enzymes from non‐catalytic scaffolds.Through it all, Danny retained his sense of joy and wonder at the “beautiful aspects of Nature’s chemistry”. This includes his discovery of an exquisite molecular specificity mechanism mediated by a single, short H‐bond that enables microbes to scavenge phosphate in arsenate‐rich environments. In recent years, he deciphered the biosynthetic mechanism of dimethyl sulfide, “the smell of the sea”, and homed in on the interplay between the evolution of an enzyme, its host organism, and environmental complexity. His insights into how the first proteins emerged caused tremendous excitement in the field. He established the roots of two common enzyme lineages, the Rossmann and P‐loop NTPases, as simple polypeptides, and suggested ornithine as the first cationic amino acid. Prior to his death, he published the results of another tour de force: evidence that the first organisms to utilize oxygen may have appeared much earlier than thought.His work impacted many research fields, and he won many significant awards. Most recently, Danny was awarded the EMET Prize for Art, Science and Culture (2020), informally dubbed “Israel’s Nobel Prize”. He was an active and valued member of the EMBO community, having been elected in 2009, and, until his passing, served on the Editorial Advisory Board of EMBO Reports.Danny was also a superb science communicator. Both his research articles and reviews are a joy to read. What stood out just as much as his brilliance was his personality, as he embodied the Yiddish concept of being a true “mensch”. Danny was humble, was down‐to‐earth, and treated all his colleagues—including the most junior members of our research teams—as equals. He championed the careers of others, both those who worked directly for him and those who were lucky enough to be “just” his friends and collaborators. He believed in us even when we did not believe in ourselves, and he was always there to answer questions both scientific and professional. While he loved to share his own ideas, he would be just as excited about ours. Despite his own busy schedule, he always found the time to help others. He was also excellent company, with a great, very dry, sense of humor, and endless interesting stories, including from his own colorful life. In the days after his untimely death, an often‐repeated phrase was “he was my best friend”. Danny’s former group members have gone on to be highly successful in both industry and academia, including more than 15 former doctoral and postdoctoral researchers who are now faculty. The network of researchers Danny has trained, mentored, or influenced is broad, and this legacy is testament to his qualities as both a scientist and a person.Danny was born in Jerusalem to an Iraqi Jewish family, and his Arabic Jewish identity was important to him. He believed strongly in coexistence and peace, and very much valued the Arabic part of his heritage. In his own words: “I am an Israeli, a Jew, an Arab, but first and foremost a human being”. He would often speak of the achievements of his children with immense pride. Danny also had a passion for being outdoors, especially climbing and hiking—when the best discussions were often to be had (Fig ​(Fig1).1). One of the easiest ways to persuade him to come for a seminar, a collaborative visit, or a conference was to have access to high‐quality climbing in the area. He passed away in a tragic rock‐climbing accident, doing what he loved most outside of science. Our thoughts are with his partner Ita and his children, and we join the much broader community of friends, collaborators, and colleagues whose hearts are broken by his sudden loss.Open in a separate windowFigure 1Dan Salah Tawfik (1955–2021)Photo courtesy of Prof. Joel Mackay, The University of Sydney.     

Garland Allen,Thomas Hunt Morgan,and Development

Garland E. Allen’s 1978 biography of the Nobel Prize winning biologist Thomas Hunt Morgan provides an excellent study of the man and his science. Allen presents Morgan as an opportunistic scientist who follows where his observations take him, leading him to his foundational work in Drosophila genetics. The book was rightfully hailed as an important achievement and it introduced generations of readers to Morgan. Yet, in hindsight, Allen’s book largely misses an equally important part of Morgan’s work – his study of development and regeneration. It is worth returning to this part of Morgan, exploring what Morgan contributed and also why he has been seen by contemporaries and historians such as Allen as having set aside some of the most important developmental problems. A closer look shows how Morgan’s view of cells and development that was different from that of his most noted contemporaries led to interpretation of his important contributions in favor of genetics. This essay is part of a special issue, revisiting Garland Allen's views on the history of life sciences in the twentieth century.     

The Mechanism of Amino Acid Activation: the Work of Mahlon Hoagland

Enzymatic Carboxyl Activation of Amino Acids(Hoagland, M. B., Keller, E. B., and Zamecnik, P. C. (1956) J. Biol. Chem. 218, 345–358)Mahlon Bush Hoagland was born in Boston, Massachusetts in 1921. He attended Harvard University and graduated in 1943. Knowing that he wanted to be a surgeon, Hoagland then enrolled at Harvard Medical School. However, he was diagnosed with tuberculosis, and his poor health prevented him from becoming a surgeon when he received his M.D. in 1948. Instead, he accepted a research position at Massachusetts General Hospital. In 1953, he became a postdoctoral fellow with Journal of Biological Chemistry (JBC) Classic author Fritz Lipmann (1) at Huntington Laboratories (also at Massachusetts General Hospital), and a year later, he moved to an adjoining laboratory to work on protein synthesis with JBC Classic author Paul Zamecnik (2).Open in a separate windowMahlon HoaglandInspired by Lipmann''s insights into acyl activation mechanisms, Hoagland used a cell-free system created by Zamecnik that carried out net peptide bond formation using ¹⁴C-amino acids (3) to uncover the mechanism of amino acid activation. As reported in the JBC Classic reprinted here, he isolated an enzyme fraction that, in the presence of ATP and amino acids, catalyzed the first step in protein synthesis: the formation of aminoacyl adenylates or activated amino acids. Using data from analysis of this fraction, Hoagland presented a scheme for amino acid activation in his Classic paper.A few years later, Zamecnik and Hoagland discovered a molecule that is essential for protein synthesis: tRNA. This discovery is the subject of the Zamecnik Classic (2).After the discovery of tRNA, Hoagland spent the next year (1957–1958) at Cambridge University''s Cavendish laboratories working with Francis Crick. During that year he traveled to France to visit the Institute Pasteur in Paris. Experiments begun at the Institute would, by 1960, lead to the discovery of messenger RNA (mRNA).When he returned to the United States, Hoagland was appointed associate professor of microbiology at Harvard Medical School. He remained there until 1967 when he accepted a position as professor at Dartmouth Medical School. In 1970, he became the director of the Worcester Foundation for Experimental Biology, a Massachusetts research institute founded by his father. He retired in 1985 and currently lives in Thetford, Vermont.Hoagland has received several awards and honors in recognition of his contributions to science. These include the 1976 Franklin Medal, the 1982 and 1996 Book Awards from the American Medical Writers Association, and membership in the American Academy of Arts and Sciences and the National Academy of Sciences.     

Ernst Mayr—Intellectual leader of ornithology

Ernst Mayr (1904–), naturalist and ornithologist since his early youth, is one of the architects of the synthetic theory of evolution of the 1940s. His main contribution was the analysis of the origin of species, i.e. the causes of biodiversity. The historical roots of these ideas reach far back to the early 1920s, when the 19-year-old student suggested to his mentor, Dr. Erwin Stresemann (Berlin), the development for birds of a theory of geographical variation and of the species. During the 1930s, Mayr himself assembled data for a comprehensive analysis of geographical variation and speciation in birds, when he studied the rich collections of the Whitney South Sea Expedition from the islands in the Pacific Ocean. He described from this and other regions 27 new species and 445 new subspecies of birds, more than any other living ornithologist. He established the basic principles of island biogeography, discussed critically the former existence of landbridges and emphasized that, in zoogeographical studies, instead of fixed regions, it is necessary to think of fluid faunas. His theoretical framework included active jump dispersal of birds and other animals as well as various types of vicariance processes which had an effect on faunal differentiation. Although Mayr was not the originator of the biological species concept, he demonstrated its validity more convincingly than anyone else before and proposed a superior and concise definition of the biospecies which everybody adopted. He also initiated with various studies a period of renewed interest in the macrosystematics of birds.Communicated by F. BairleinDedicated to Professor Ernst Mayr in admiration and friendship on the occasion of his 100th birthday on 5 July 2004     

The Philosophy of Donald T. Campbell: A Short Review and Critical Appraisal

Aside from his remarkable studies in psychology and the social sciences, Donald Thomas Campbell (1916–1996) made significant contributions to philosophy, particularly philosophy of science,epistemology, and ethics. His name and his work are inseparably linked with the evolutionary approach to explaining human knowledge (evolutionary epistemology). He was an indefatigable supporter of the naturalistic turn in philosophy and has strongly influenced the discussion of moral issues (evolutionary ethics). The aim of this paper is to briefly characterize Campbells work and to discuss its philosophical implications. In particular, I show its relevance to some current debates in the intersection of biology and philosophy. In fact, philosophy of biology would look poorer without Campbells influence. The present paper is not a hagiography but an attempt to evaluate and critically discuss the meaning of Campbells work for philosophy of biology and to encourage scholars working in this field to read and re-read this work which is both challenging and inspiring.