Some statistical aspects of sampling in morphometry

Morphometry requires, in addition to the accurate counting of points, intersections and transections, meticulous attention to sampling. Methods are described and discussed for ensuring that adequate samples are obtained for a given standard error. For all situations in which stratification is used, the importance of increasing the number of the early strata for reducing the variance is emphasized.     

Some fundamental aspects of epidemiology: a guide for laboratory scientists.

Epidemiologic methods used to study human diseases are often unfamiliar to the laboratory scientist. This paper outlines the standard method by which epidemiologic studies are classified, explains the methodologic strengths and weaknesses of different kinds of studies, and notes the kinds of inferences that can be drawn from each. Surveys on populations are treated first, followed by sample surveys. Prospective (follow-up) studies, in which groups of subjects are followed in time, are a basic epidemiologic method. Alternatives to these studies that do not require similar time commitments but may allow similar inferences are record studies. Retrospective, or case-control studies, are often the only feasible method for studying rare diseases. However, diseases with long latency periods and problems in control selection can make these studies difficult to analyze and interpret.     

Studies on Ligula intestinalis Some aspects of the pathology in the second intermediate host

A 3 year survey of a lake, in which 120 roach, Rutilus rutilus , were examined revealed the presence of the plerocercoids of Ligula intestinalis in more than 90 % of the fish. The average number of parasites per fish was 4.2 although fish exceeding 32 g were not ligulosed. Gudgeon, Gobio gobio , of all sizes were affected. Implants of the plerocercoids into small roach, gudgeon and goldfish, Carassius auratus , were successful but not in the case of Perca fluviatilis, Esox lucius and Leuciscus cephalus. The pathological effects of the plerocercoids on roach and gudgeon are described.     

Some aspects of clinical relevance in the maturation of respiratory control in infants.

Two reflex mechanisms important for survival are discussed. Brain stem and cardiovascular mechanisms that are responsible for recovery from severe hypoxia (autoresuscitation) are important for survival in acutely hypoxic infants and adults. Failure of this mechanism may be important in sudden infant death syndrome (SIDS), because brain stem-mediated hypoxic gasping is essential for successful autoresuscitation and because SIDS infants appear to attempt to autoresuscitate just before death. A major function of another mechanism is to protect the airway from fluid aspiration. The various components of the laryngeal chemoreflex (LCR) change during maturation. The LCR is an important cause of prolonged apneic spells in infants. Consequently, it also may have a role in causing SIDS. Maturational changes and/or inadequacy of this reflex may be responsible for pulmonary aspiration and infectious pneumonia in both children and adults.     

Informational aspects of telepathology in routine surgical pathology.

Application of computer and telecommunication technology calls serious challenges in routine diagnostic pathology. Complete data integration, fast access patients' data to usage of diagnosis thesaurus labeled with standardized codes and free text supplements, complex inquiry of the data contents, data exchange via teleconsultation and multilevel data protection are required functions of an integrated information system. Increasing requirement for teleconsultation transferring a large amount of multimedia data among different pathology information systems raises new questions in telepathology. Creation of complex telematic systems in pathology requires efficient methods of software engineering and implementation. Information technology of object-oriented modeling, usage of client server architecture and relational database management systems enables more compatible systems in field of telepathology. The aim of this paper is to present a practical example how to unify text based database, image archive and teleconsultation in a frame of an integrated telematic system and to discuss the main conceptual questions of information technology of telepathology.     

Variability of dry mass as a fundamental biological property demonstrated for the case of Vaccinia virions.

The dry mass of individual vaccinia virions, as an example of a presumably uniform biological population, prepared in different lost at the Institute for Tropical Hygiene in Hamburg, was tested for variability by quantitative electron microscopy. A value of 5.26 X 10(-15) g for the median weight of the particle was calculated from 7,300 determinations. By assessing the variability of polystyrene latex spheres, which were used as mass standards, we demonstrated that the variability of dry mass of vaccinia virions is fivefold greater than the variability (standard) introduced by the method for determining mass. It was concluded that while genetic control in a presumably homozygous virion is strict with respect to quality, quantity of viral components (other than DNA) varies in fashion that can be aptly described by a log-normal distribution. It is recognized that this observation is empirically supported by the paradigm that any composite biological entity is subject to quantitative variability, the more so the heavier the individual representatives of a species are. In addition, the effects that extractions and staining have on the dry mass of vaccinia are reported, as well as is the median for the dry mass of other strains of pox viruses.     

Intercellular communication and some structural aspects of membrane junctions in a simple cell system

Summary AChironomus salivary gland consists of a chain of 30 giant cells (G-cells) and 4 to 6 flat cells (F-cells) spanning a lumen. The surface membranes of these cells are linked by two kinds of organized structures: theseptate junction, taking up nearly the entire surface of cell contact, and thegap junction, occupying a small fraction of this surface. (These junctional structures are examined in the electron microscope after La infiltration.) All cells are joined to their immediate neighbors by septate junctions, the G- to G-cells, the F- to F-cells, and the F- to G-cells; the G-cells, at least, are also joined by gap junctions. All cells are also in communication with each other: small inorganic ions, fluorescein (mol. wt. 330) and Procion Yellow (mol. wt. 550) pass from one cell interior to the next.     

Some aspects of corticosteroid-induced cleft palate: a review.

Since the discovery 25 years ago that cortisone can produce cleft palate in mouse embryos investigations into possible mechanisms of this corticosteroid-induced defect have been many and varied. However, the teratogenic mode of action remains not fully clarified. It is with this thought in mind that we have reflected upon what is known concerning corticosteroids and cleft palate. The major metabolic pathways upon which glucocorticoids act as well as their intracellular mode of action are well known. Differential sensitivity of various mouse strains to cortisone treatment as well as recent results from interstrain blastocyst transfer experiments demonstrate that corticosteroid action is influenced by both the fetal and maternal genomes. Labeling experiments indicate that corticosteroid-induced cleft palate is the result of direct action of the steroid molecule on the fetus, whose own sensitivity to insult, perhaps owing to differences in binding of corticosteroids to tissue proteins, determines the final effect. Possible mechanisms that have been proposed by which corticoids may produce cleft palate include: disruption of glycosaminoglycan or collagen synthesis or both, intracellular lysosomal membrane stabilization, myopathy, weakened midline fusion, and loss of amniotic fluid. Also discussed is the role of stress and stress-induced corticosteroids and their possible role in the production of cleft palate.     

Some unexamined aspects of analysis of covariance in pretest-posttest studies

The use of an analysis of covariance (ANCOVA) model in a pretest-posttest setting deserves to be studied separately from its use in other (non-pretest-posttest) settings. For pretest-posttest studies, the following points are made in this article: (a) If the familiar change from baseline model accurately describes the data-generating mechanism for a randomized study then it is impossible for unequal slopes to exist. Conversely, if unequal slopes exist, then it implies that the change from baseline model as a data-generating mechanism is inappropriate. An alternative data-generating model should be identified and the validity of the ANCOVA model should be demonstrated. (b) Under the usual assumptions of equal pretest and posttest within-subject error variances, the ratio of the standard error of a treatment contrast from a change from baseline analysis to that from ANCOVA is less than 2(1)/(2). (c) For an observational study it is possible for unequal slopes to exist even if the change from baseline model describes the data-generating mechanism. (d) Adjusting for the pretest variable in observational studies may actually introduce bias where none previously existed.     

Trapping, loss and annihilation of excitations in a photosynthetic system. I. Theoretical aspects

In this paper are discussed a few theoretical aspects of the transfer, trapping, loss and annihilation of excitations as they occur in a photosynthetic system after a picosecond light pulse. A random-walk model is introduced to describe the dynamical behavior of the excitations in a domain and is used to calculate the parameter that determines the shape of the total fluorescence yield vs. pulse intensity curve in the case in which the reaction centers are all in the closed state (Paillotin, G., Swenberg, C.E., Breton, J. and Geacintov, N.E. (1979) Biophys. J. 25, 513–533). It is shown that this parameter depends critically on the number, λ, of connected photosynthetic units in a domain. A master equation is postulated to describe the decay of the excitations in the case where the transition of the reaction center from the open to the closed state, induced by the capture of an excitation, is included. The trapping and loss of excitation in a mixture of open and closed reaction centers, generated in the course of the transfer process, is assumed to be described by an equation that is the equivalent for a single domain of the Vredenberg-Duysens relation (Vredenberg, W.J. and Duysens, L.N.M. (1963) Nature 197, 355–357). The master equation is used to find the total probability of loss per excitation, U_λ(z), and the total fraction of reaction centers closed, V_λ(z), as a function of the average number of excitations z created in a domain when the reaction centers are all in the open state before the pulse. It is shown that, for most photosynthetic systems, an increase of U_λ(z) with z can occur only if λ 3. It is further concluded that the combined measurement of U_λ(z) and V_λ(z) can give detailed information about λ and the parameters involved in the transfer process.     

Some aspects of metabolism following a 35 km road run.

The metabolism of eight men (mean: age, 26.0 years; maximal oxygen consumption, 65.0 ml.kg-1.min-1; body fat, 10.3%) was measured on counterbalanced control (baseline values for 8 h) and experimental (post 35 km run values for 8 h) days. The excess postexercise volume of oxygen consumed of 32.37 l and increase in energy used of 594 kJ during the 8 h after completion of the run were equivalent to average increases of 23.7 and 21.1%, respectively, when compared with time-matched controls. Furthermore, the oxygen uptake and energy expenditure were still elevated by 12.7 (P less than 0.0005) and 9.7% (P = 0.001), respectively, at the end of this period but the fact that they had returned to baseline 24 h after the 35 km road run contrasts with some reports in the literature that metabolism is still elevated at this time following less demanding exercise intensities. Rectal temperature was elevated by 2.3 degrees C at the end of the run but the difference had decreased to 0.2 degrees C by 7 h postexercise. The respiratory exchange ratio and changes in blood metabolites (nonesterified fatty acids, glycerol and ketone bodies) indicated a greater postexercise utilisation of fat notwithstanding a 6300 kJ meal ingested on both control and experimental days. The highest measured serum creatine kinase enzyme activity of 1151 U.l-1 (P less than 0.05) occurred 24 h postexercise, as compared with the control value of 145 U.l-1, and indicates the possibility of skeletal muscle damage.