. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Amoeboid Movement 635 the tension of 20 dynes/cm. at the interface of olive oil and water.^" The tensions measured by Harvey and Marsland are not "surface tension" but total restraining tension residing in the cell periphery; there is no rigorous distinction in such a system between contractile and elastic tension. Calcu- lations indicate that tensions of 1 to 3 dynes/cm. are of the order of magni- tude needed to force the sol forward,^^ but an amoeba can develop much greater tensions, as when it
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Amoeboid Movement 635 the tension of 20 dynes/cm. at the interface of olive oil and water.^" The tensions measured by Harvey and Marsland are not "surface tension" but total restraining tension residing in the cell periphery; there is no rigorous distinction in such a system between contractile and elastic tension. Calcu- lations indicate that tensions of 1 to 3 dynes/cm. are of the order of magni- tude needed to force the sol forward,^^ but an amoeba can develop much greater tensions, as when it pinches a Paramecium in two.^^ The contractile tension of the gel presumably resides in long protein mole- cules whose organization and "contractility" is indicated by measurements 7o )oo 9o 8o ?o 6o 5o 40 30 20 lO. 10 *K lo' Fig. 241. Proportionality between the effects of hydrostatic pressure on protoplasmic streaming (and cell division) and the degree of solation imposed by pressure in various gel systems. ⢠arbitrary point, all other values relative to this; -p gel value, amoeba; -^ gel value, unfertilized Arbacia eggs; X gel value, cleaving Arbacia eggs; + rate of cleavage, Arbacia eggs; ⢠gel value, Elodea cells; O rate of streaming, Elodea cells; M gel value, actomyosin gel (rabbit muscle at pH , 23°-24° C). Redrawn from Marsland 1942 and 1944.^" 'â ' of resistance to granule movement in a centrifugal field, and by observation of the effects of hydrostatic pressure. The gel of newly formed or advancing pseudopods is less rigid than the gel in posterior regions. When amoebae are subjected to high hydrostatic pressure the "viscosity" falls, the gel so- lates and locomotion stops. At 2000 pseudopods are long and cylin- drical; above 6000 no new pseudopods are formed; at about 6500 ^ terminal spheres appear on pseudopods and the pseudopods retract as balls of fluid. A series of functionsâamoebo
Size: 1664px × 1502px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisher, booksubjectphysiologycomparative
