250 



The Structure of Protoplasm 



W^ 



is to be had in the migration of fibroblasts shown in moving pictures 

 by Dr. Warren Lewis. As the fibroblasts move, they form long 

 streamers attached to the substratum. These are later torn loose, or 

 broken, and then snap and recoil rapidly. 



The elasticity of protoplasm varies, just as do its other physical 



properties such as viscosity. Highly 

 viscous protoplasm may be poorly 

 elastic, resembling plastic paste, 

 whereas thin protoplasm is sometimes 

 capable of great extensibility, with 

 pronounced recoil. From the fore- 

 going it could be assumed that vis- 

 cosity and elasticity have a direct 

 bearing upon each other, but this is 

 not true; they are independent vari- 

 ables. 



Very thin protoplasm is often 

 thought to be inelastic because the 

 elasticity cannot be readily deter- 

 mined. 



That thin solutions may be highly 

 elastic is capable of nice demonstra- 

 tion in soap solutions.'' Sodium stea- 

 rate will, under favorable conditions, 

 exhibit pronounced elasticity though 

 the solution is but twice as viscous 

 as water. The elastic quality of so 

 thin a solution inay be demonstrated 

 by twirling the flask containing it and 

 observing the manner in which the 

 solution comes to rest. A wholly inelastic liquid, such as water or 

 glycerin, will come to rest slowly and show no return, but an elastic 

 solution will slow down, come to a sudden stop, and then return a 

 part of the circumference of the flask. Were it possible to apply some 

 such method to protoplasm, I feel confident that the thinnest proto- 

 plasm would show elastic qualities just as does the thicker protoplasm 

 in which elasticity is so readily demonsti'ated. 



The effects of salts on the elasticity of protoplasm have been 

 determined; calcium increases the extensibility of protoplasm. 



Fig. 2. The stretching of proto- 

 plasm with a microneedle. On 

 tearing, the protoplasm rebounds, 

 exhibiting high extensibility, ten- 

 sile strength, and recoil. 



' Third Colloid Symposium Mono., New York. 1925. 



