VISCOSITY 221 



results between workers may have been due to technique or to 

 difficulty in distinguishing stages in mitosis in living eggs. 



Changes in protoplasmic consistency can be induced by 

 external factors such as temperature and salts. Those observed 

 are the result of laboratory experiments, but many are probably 

 duplicated in nature. The viscosity of gelatin falls with rise in 

 temperature. Lecomte duNoiiy found the same to be true for 

 blood serum the viscosity of which falls from a value of 490 at 

 20°C. to 240 at 56°C. F. Weber finds that the viscosity of plant 

 protoplasm decreases with rise in temperature. 



The effect of salts on the consistency of protoplasm has been 

 extensively studied, but there is little agreement in the experi- 

 mental results. It does appear, however, that sodium ordinarily 

 lowers viscosity and that calcium raises it. Other protoplasmic 

 changes produced by these elements support this deduction, 

 viz., that sodium disperses, and calcium aggregates; thus, sodium 

 increases the permeability of the cell, and calcium (usually) 

 decreases it; calcium is necessary for membrane formation; i.e., 

 it coagulates or aggregates the surface protoplasm, while sodium 

 has no influence. 



As in the case of most experimental results obtained on the 

 effects of salts on protoplasm, the statement that calcium tends 

 to gelate (thicken) and sodium to solate (thin) is met with denial; 

 however, the majority opinion holds that calcium increases 

 protoplasmic viscosity while sodium either lowers it or has no 

 appreciable influence. But no general rule can be stated, for 

 there is no definite physicochemical entity that we can call 

 protoplasm. Not only does the protoplasm of species differ 

 but that of tissues and of adjoining cells as well. While so com- 

 plex and varied a system as protoplasm is likely to show diverse 

 viscosity changes brought on by the same salt, yet such may 

 occur in much simpler (nonliving) systems and in so comphcated 

 a way as to give irregular curves ; the same salt may increase and 

 decrease viscosity. 



Acids have an aggregating effect on protoplasm. Living nuclei 

 may be coagulated by acid, as indicated by a granular appear- 

 ance, and yet remain alive. The coagulation may be reversed 

 by bringing the cell back to a neutral condition; normal growth 

 then continues. Heretofore, coagulation has been regarded as 



