Some Physical Properties of Protoplasm 249 



in slime molds all the protoplasm sets thixotropically when anes- 

 thetized. 



A neurologist, on observing the instantaneous cessation of move- 

 ment of slime mold protoplasm when anesthetized by carbon 

 dioxide, characterized it as paralysis. I find the analogy interesting, 

 though prefer not using the term simply because less is known of 

 the mechanism of paralysis than of anesthesia. It may be true, 

 however, that paralysis, like anesthesia, is due to a thixotropic set- 

 ting of the protoplasm of nerve fibers. 



Thixotropic gels possess large quantities of water, often with less 

 than 1 per cent of solid matter. A germanium or cadmium gel may 

 have as much as 99.8 per cent water. The jelly-fish contains but 2 or 

 3 per cent solid matter, yet maintains its form. Such systems must 

 be built of long and flexible fibers in order to set into firm and 

 elastic gels. Fibers may contact each other at greater distances than 

 do spheres, therefore, fewer units are needed to build a structure 

 of given volume. 



Further evidence of a very open structure in certain jellies is 

 the transparency of some of them. Soap jellies are quite clear. This 

 is possible because of an open three-dimensional lattice built of long 

 fibrous units. The sudden locking of such intermeshing fibers 

 accomplishes thixotropic setting; and their release by mechanical 

 agitation is thixotropic collapse. In protoplasm, these linear units 

 are the familiar polypeptide chains. 



ELASTICITY 



That protoplasm is elastic is so obvious to many workers that one 

 wonders why it should ever have been questioned by others. The 

 earliest students of protoplasm knew it to be elastic. Additional 

 evidence of recent date comes from Northen" and Norris". 



Proof of the elasticity of protoplasm is to be had in a number of 

 ways. The simplest is to stretch it with microneedles (Fig. 2) . On 

 release after stretching, the protoplasm usually shows pronounced 

 recoil, indicating high elastic qualities. 



The elasticity of protoplasm may be demonstrated in another and 

 rather novel way, by inserting a metal particle and attracting it 

 electromagnetically. On elimination of the electromagnetic field the 

 particle retraces its path due to the elasticity of the protoplasm. 

 Evidence that the elastic qualities of protoplasm are not pathological 



Protoplasma 31, 1-8. 1938. 



J. Cell, and Comp. Physiol., 16, 313. 1940. 



