Comparative biochemistry and physiology最新文献

1. Free amino acid composition is examined in six copepod species occurring along a salinity gradient that extends from the open ocean to fresh water.

2. Salinity accounts for half of the variation in total concentration. The remainder results from seasonal temperature change and associated variables.

3. Going from a marine species, through a series of three estuarine species, and finally to a fresh water representative, the basic amino acids become more important, whereas glycine, alanine and taurine decrease. The result is a comparatively uniform pattern of composition in fresh water. This relationship is expresed by an index of biochemical dominance.

1. The increase in body weight of Hymenolepsis diminuta in diluted Hank's saline is entirely due to the intake of water. There is some salt loss, but this is of negligible weight.

2. Salt loss and water intake are proportional to the dilution of the medium.

3. It is concluded that H. dimimuta is an osmoconformer and that the protonephridial canals have no osmoregulatory function.

1. The polar bear has developed thermoregulatory mechanism consistent with its semiaquatic way of life.

2. In vivo examinations of three adult polar bears were performed by radiotelemetry on bears in cages and by measurements on bear tied to a frame in air and in water.

3. Significant insulation is achieved by means of fur, blubber and other peripheral tissues both in air and water.

4. Vascular heat exchanges are present in the limbs, and two thin muscle sheets adjacent to the skin probably afford a special avenue of heat dissipation.

5. Insulation and heat dissipation seems, however, insufficient during extreme weather conditions, forcing the polar bear to utilize postural increase of insulation or to slow down activity during cold or warm weather respectively.

1. The anatomy of the cephalic ganglion and associated nerves in the Acanthocephalan Macracanthorhynchus hirudinaceus has been studied preliminary to use of the organ as a model system for the study of neural pathways.

2. Analysis of routine serial sections of the anterior portion of the worm revealed the existence of eighty-six cells within the cephalic ganglion itself.

3. There are six pairs of nerves with bilateral symmetry which exit from the ganglion. The total number of neurons contained within the six pairs of nerves is approximately seventy-two.

4. This investigation reveals that certain anatomical features are either new or different from that which has been proposed by earlier workers. Among these observations are the following: (a) The anterior ventral nerve does not branch but is always two separate bundles of neurons. (b) The anterior ventral nerve is not wrapped in muscle as is the lateral posterior nerve after it leaves the thick layer of the dorsal receptacle. (c) The paired lateral posterior nerve consists of two bundles of neurons with approximately twenty-three neurons/bundle. (d) The lateral posterior nerve originates exclusively from the dorsal concave surface of the brain and never from the convex or ventral surface.

1. The mechanism of water absorption by cricket eggs is discussed.

2. On the basis of the available evidence, water absorption appears to involve changes in the properties of the shell.

1. During forward walking parapodial stepping and s waves occur; the two can be separated by sectioning appropriate segmental nerves.

2. Thirty cycles of stepping begin at the pygidium/min and move rostrally over 3–10 segments/sec.

3. Ipsi- and contralateral cycles are about 180° out of phase, a phase lag developing during acceleration.

4. Pacemakers are in each nerve cord segment; the frequency is determined by dominant posterior pacemakers.

5. Propagation of locomotory cycles depends upon and intact cord and intact parapodial nerves and ganglia in each segment, and does not require the integrity of other segmental nerves, setal receptor input nor peripheral reflexes.

1. Activities of various enzymes were measured in birds drinking fresh water and in birds adapting to 200 mM salt water.

2. Although an increase in the activity of all enzymes was measured in ducks on salt water as compared to their freshwater controls, the probable rate limiting enzyme, phosphofructokinase, showed the greatest increase (three- to fourfold).

3. The correlation between the changes of the ATPase and phosphofructokinase enzyme activities supports the idea that the glycolytic pathway plus associated cycles supply a major proportion of the ATP needed by the transport enzyme.

1. Changes in the concentrations of calcium and bicarbonate in the blood of hydrated Helix aspera, exposed to raised tensions of carbon dioxide or injected with HCl, NaHCO₃ or CaCl₂, were qualitatively those to be expected if the blood were in equilibrium with solid calcium carbonate.

2. However, the blood was found to be greatly supersaturated with respect to calcite and aragonite, even allowing for the presence of unionized calcium.

3. Concentrations of calcium in the blood of control snails showed a marked correlation with total concentrations of blood solutes.

4. Potassium levels were unchanged by hypercapnia and by the injection of CaCl₂ or NaHCO₃, but rose following the injection of HCl. Raising the concentration of potassium in the blood brought about an increase in the concentration of calcium without significant change in bicarbonate.

1. The fractional distribution of ¹³⁷Cs was determined in rats forced to swim in warm (37°C) and cold (22°C) water.

2. This was done in order to determine the possible effect of changes in muscle blood flow on the gastrocnemius muscle to arterial blood lactate diffetence previously observed in the cold water swimming rat.

3. The results indicated that the muscle blood flow was similarly elevated in both 22 and 37°C rats at the time when there was a large difference between muscle and blood lactate only if the 22°C swims.

4. Therefore, the greater differene in lactate concentration between gastronemius muscle and arterial blood observed in cold water swimming rats, cannot be accounted for by low muscle blood flow.

1. Glutamate-aspartate transaminase activity in homogenates of young adults is reported for stocks of Drosophila melanogaster, D. immigrans, D. pseudoobscura and D. willistoni grown at 15 and 25°C.

2. Female D. melanogaster acclimated at 25°C, have lower glutamate-aspartate transaminase activity, measured at 20°C, than do those grown at the “normal” temperature of 15°C.

3. Glutamate-aspartate transaminase activity of young adult males and females of D. immigrans acclimated at 25°C is lowe than that of flies grown at 15°C when measured at 20°C.

4. Transaminase activity does not vary with acclination temperature in young adults of the two stenothermal species, D. pseudoobscura and D. willistoni.

5. The data reported support the theory that eurythermal species at Drosophila have greater capacity for physiological adaptation than do stenothermal species. It is theorized that respiratory control in Drosophila may be related to rates of amino acid conversion and the level of substrates entering the Krebs cycle.