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 



PRESSURE- LBS./lN*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 6.5, 23°-24° C). Redrawn from Marsland 

 1942 and 1944.^" '■' 



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 lb/in.- pseudopods are long and cylin- 

 drical; above 6000 Ib./in.- no new pseudopods are formed; at about 6500 

 Ib./in.^ terminal spheres appear on pseudopods and the pseudopods retract 

 as balls of fluid. A series of functions— amoeboid movement, chromatophore 



