PROTEINS 493 



electric shock, was an example of a pronounced increase in the 

 consistency of protoplasm, but whether gelatinization, coagula- 

 tion, or an increase in viscosity involving neither of these changes 

 occurred cannot be said. Cessation of the Brownian movement 

 of the protoplasmic particles indicated a change toward a more 

 viscous state. Too severe an electric shock caused a definite 

 and permanent gelation (coagulation) and death. A mild shock 

 was followed by solation, slowly accomplished by the amoeba 

 itself after the current was released. The phenomenon may have 

 been a pure thixotropic one, identical with that occurring in 

 gels. Freundlich and Rawitzer have shown that an electric 

 current will bring about the gelation of a thixotropic sol (Karrer 

 has shown that a current may have the opposite effect and solate 

 a gel). The change in consistency involved in the locomotion 

 of an amoeba is, according to S. O. Mast, simply a rhythmic 

 solation and gelation of the protoplasm. All such changes 

 probably do not involve coagulation. A more convincing case 

 of true and reversible coagulation in protoplasm is that resulting 

 from the addition of acid. M. A. van Herwerden finds that, 

 normally, no structure is visible in the living nuclei of the 

 mesenchyme and nerve tissue in the tail of the living tadpole, 

 nor is a nuclear membrane to be seen (it is often impossible to 

 locate even the nucleus); but if the tadpole is put into water 

 that has been acidified (0.05 part of acetic acid to 100 parts of 

 water), the nuclei assume a clearly defined contour and a granular 

 structure, and return to normal when placed in pure water; they 

 have been reversibly coagulated. If a cell is dividing, the acid 

 renders the spireme or the chromosomes visible. Other struc- 

 tures, such as mitochondria, invisible before, appear in the sur- 

 rounding cytoplasm. If the tadpole is now placed in pure pond 

 water, the structures described soon disappear. The acid has 

 produced a reversible coagulation without any apparent or 

 permanent ill effect on the protoplasm. 



The gelation of protoplasm by injected salts is another interest- 

 ing case. Kerr has shown that when a calcium salt is injected by 

 micropipettes into the root hairs of the aquatic plant Limnobium, 

 the salt may cause the protoplasm to form an irreversible 

 coagulum or a reversible jelly or both, in different regions of the 

 same cell. Coagulation (irreversible gelation) always takes 

 place at the point of injection where the calcium salt is most 



