Dissolved phosphorus concentrations in a natural salt-marsh of Delaware

Summary Dissolved phosphorus concentrations, salinity, pH, and related physical parameters were used to evaluate the variations in a natural salt-marsh. Diel, tidal, lunar, and seasonal variations in phosphorus concentrations were evaluated for a three year period in a natural marsh, situated along the southwestern coast of the Delaware Estuary.Seasonal concentrations of dissolved phosphorus reached a maximum during the summer months (150 g at .l^-1) and a minimum during the winter months (10 g at .l^-1). An equation representing the relationship of the measured parameters to the dissolved phosphorus concentrations is presented. Several mechanisms are postulated to explain the seasonal fluctuations in the phosphorus concentrations.

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Résumé Les concentrations dissous de phosphore, la salinité, le pH, et quelques parametres physiques étaient utilisés à évaluer les variations dans un marais salant. Les variations quotidiennes, lunaires, saisonnières et les variations des marées dans les concentrations de phosphore étaient évalués pendant trois années dans un marais salant qui se trouve le long de la côté sud-ouest de l'estuaire de Delaware.Les concentrations saisonnieres de phosphore dissous ont atteint le maximum pendant les mois d'été (150 g at .l^-2) et un minimum pendant les mois d'hiver (10 g at .l^-2). Une équation qui représente le rapport des paramètres mesurés aux concentrations dissous de phosphore est présentée. Quelques méchanismes sont postulés à expliquer les fluctuations saisonnieres dans les concentrations de phosphore.

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Contribution No. 65 from the Marine Laboratories, University of Delaware, Newark, Delaware. Contribution No. 207 from the Marine Institute, The University of Georgia, Sapelo Island, Georgia.     

Resistance of Escherichia coli to tetracyclines. Changes in permeability to tetracyclines in Escherichia coli bearing transferable resistance factors

1. When strains of Escherichia coli, bearing transferable factors for resistance to the tetracyclines (R-factors), and previously cultured in the absence of the tetracyclines, are grown for 15–30min. in a low, subinhibitory, concentration (10μg./ml.) of oxytetracycline or tetracycline, there is a rapid and striking increase in resistance to oxytetracycline or tetracycline, this being associated with a marked fall in the absorption of the drug by the cells. 2. Very short preincubation (1min.) with oxytetracycline, followed by growth for 15–30min. in drug-free medium, produces a marked fall in the absorption of the drug by the resistant cells. Preincubation for 30min. with very low concentrations (0·05μg./ml.) of oxytetracycline produces a similar effect. 3. β-Apo-oxytetracycline, which has very little antibacterial activity, also induces a decreased absorption of oxytetracycline. 4. The ability to exclude oxytetracycline is retained by preincubated resistant cells after growth for 2hr. in drug-free medium. However, after growth for 16hr. in drug-free medium, the cells absorb oxytetracycline freely. 5. Chloramphenicol and proflavine inhibit the adaptive decrease in tetracycline absorption. 5-Fluorouracil has only a slight effect. 6. Spheroplasts prepared from resistant cells show an impaired response to preincubation with tetracycline, compared with intact cells. 7. The relevance of these results to the probable mechanism of tetracycline resistance in R-factor-bearing E. coli is discussed.     

Limitations on Complexity of Random Learning Networks

Randomly connected networks can be made adaptive, and thus able to “learn.” Signal-to-noise considerations are shown to limit the maximum initial complexity which can learn. A higher order of complexity may be possible in multilayered structures which learn layer-by-layer; or if learning is possible during construction. Perception-like devices would appear not to be operative if of a high order of complexity.     

CONTRACTILITY AND ULTRASTRUCTURE IN GLYCEROL-EXTRACTED MUSCLE FIBERS : I. The Relationship of Contractility to Sarcomere Length

This study was undertaken to determine whether glycerol-extracted rabbit psoas muscle fibers can develop tension and shorten after being stretched to such a length that the primary and secondary filaments no longer overlap. A method was devised to measure the initial sarcomere length and the ATP-induced isotonic shortening in prestretched isolated fibers subjected to a small preload (0.02 to 0.15 P₀). At all degrees of stretch, the fiber was able to shorten (60 to 75 per cent): to a sarcomere length of 0.7 µ when the initial length was 3.7 µ or less, and to an increasing length of 0.9 to 1.8 µ with increasing initial sarcomere length (3.8 to 4.4 µ). At sarcomere lengths of 3.8 to 4.5 µ, overlap of filaments was lost, as verified by electron microscopy. The variation in sarcomere length within individual fibers has been assessed by both light and electron microscopic measurements. In fibers up to 10 mm in length the stretch was evenly distributed along the fiber, and with sarcomere spacings greater than 4 µ there was only a slight chance of finding sarcomeres with filament overlap. These observations are in apparent contradiction to the assumption that an overlap of A and I filaments is necessary for tension generation and shortening.     

CONTRACTILITY AND ULTRASTRUCTURE IN GLYCEROL-EXTRACTED MUSCLE FIBERS : II. Ultrastructure in Resting and Shortened Fibers

Glycerol-extracted rabbit psoas muscle fibers were examined by electron microscopy both before and after ATP-induced isotonic shortening. Ultrastructural changes were correlated with the initial sarcomere length and the degree of shortening. The ultrastructural appearance of the resting fiber at rest length was identical with that described by H. E. Huxley and Hanson. At sarcomere lengths greater than 3.7 to 3.8 µ, the A and I filaments were detached and separated by a gap. The presence of "gap" filaments was confirmed, and evidence is presented which indicates that these filaments form connections between the ends of the A and I filaments. Shortening from initial sarcomere lengths at which the filaments overlapped took place through sliding of the filaments. If shortening was initiated from sarcomere lengths at which there was a gap, a narrowing of the I band was brought about by a curling of the I filaments at the boundary between the A and I bands. No evidence could be found that the I filaments moved into the A band.     

GERIATRIC PATIENTS IN A MENTAL HOSPITAL

An intensive study was made of men 55 years of age and over admitted to Napa State Hospital with either senile or arteriosclerotic brain disease. A ward treatment program, combining both the medical and psychiatric approaches, was applied to one-half of such patients admitted to a state hospital, with the aim of determining what, if any, effect this program would have on the course of the illnesses.Special laboratory studies showed: (a) Serial electroencephalograms and hospital adjustment ratings appeared to be positively correlated with the patients'' clinical course; (b) In 35 per cent of cases the electrocardiographic tracings at the time of admittance were within normal limits; (c) A “pathological level” of blood bromides was found in only one of 340 consecutive admissions in this age group.Sociopsychiatric study of 100 consecutively admitted patients revealed that: (a) 35 per cent of the patients were from the middle, and 65 per cent from the lower classes of society; (b) Only 59 per cent were admitted because of activities specifically psychotic. (c) 63 per cent needed admittance to this state hospital for observation and diagnosis, but only 44 per cent needed to stay for care and treatment; (d) In 88 per cent, specific emotional stresses were present just preceding and coincident with the clinical appearance of the organic brain syndrome.     

THE CAMBIUM AND SEASONAL DEVELOPMENT OF THE PHLOEM IN PYRUS MALUS

Evert , R. F. (U. Wisconsin, Madison.) The cambium and seasonal development of the phloem in Pyrus malus. Amer. Jour. Bot. 50(2): 149–159. Illus. 1963.—The cambium in apple consists of several layers of cells at all times, and practically all cambial cells divide periclinally one or more times before undergoing differentiation. The cambial initials do not seem to be in a uniform, uniseriate layer. Judged by collections made during 2 seasons (August, 1958–October, 1960), the seasonal cycle of phloem development is as follows. Early in April, cells in the outer margin of the cambial zone begin to differentiate into sieve elements. At approximately the same time, activity (division) commences throughout the cambial zone. By the end of July or early August, sieve-element differentiation is completed. Cessation of function begins in either late September or in October with the formation of definitive callose on the sieve areas of sieve elements in the outer margin of the functional phloem. By late November, all sieve elements are devoid of contents and most of their companion cells collapsed. Phloem differentiation precedes xylem differentiation by approximately a month and a half; xylem and phloem differentiation cease almost simultaneously; and fiber-sclereid development is coincident with the period of maximal xylem differentiation.