246 The Structure of Protoplasm 



when subjected to pressure. No vestige of the structural features 

 of the preceding karyokinetic figure remains. 



Among his many previous references to physiological examples 

 of thixotropy, Freundlich- cites an experiment by Faure-Fremiet^, 

 who found that mechanical agitation would change an Amoeba 

 from the firm condition of its resting state to the fluid condition of 

 its active state. Peterfi^ described the liquefaction of the gelled 

 protoplasm of neuroblasts caused by the movement of a needle. 



It is a pathological case of thixotropic behavior, involving not 

 collapse but the rapid setting of protoplasm, of which I wish to speak 

 in detail, and in so doing I should like to broaden the concept of 

 thixotropy so as to include the instantaneous and spontaneous set- 

 ting of a colloidal system. A truly thixotropic gel always under- 

 goes rapid gelation after collapse. As both phenomena are charac- 

 teristic of thixotropic behavior, there is no reason why emphasis 

 should be laid upon one any more than upon the other, especially, 

 since the instantaneous setting is as remarkable as the sudden 

 collapse by agitation. 



The thixotropic collapse of a gel due to agitation is a form of 

 liquefaction which is characterized by the suddenness with which it 

 takes place. Just so is the instantaneous setting of a colloidal system 

 a form of gelation or gelatinization characterized by the rapidity 

 with which it is accomplished. The occurrence of either of these 

 phenomena in living matter may be spontaneous or the result of a 

 pathological condition. As I shall refer primarily to thixotropic 

 setting, it may be well to define it as the instantaneous and readily 

 reversible gelatinization of protoplasm or other colloidal system. 



Much of the protoplasm of slime molds is in a state of continuous 

 flow. The movement is first in one direction and then in the other, 

 reversal occurring every forty-five to fifty seconds. Any pronounced 

 change in the rhythmical flow of the protoplasm is an indication of 

 a change in physiological condition. 



If subcultures of slime molds, in particular, Physarum poly- 

 cephalum, are placed in a small gas chamber and subjected to certain 

 anesthetic agents, the streaming protoplasm comes to a sudden stop. 

 Recovery takes place within a minute or two, and there is no 

 observable injury. Three anesthetics accomplish this perfectly: car- 

 bon dioxide, cyclopropane, and chloroform (Fig. 1). 



^ Chemisch Weekblaad (Amsterdam), 32, 739. 1935. 

 ' Trans. Faraday Soc, 26, 779. 1930. 

 * Arch. exp. Zellforsch., 4, 143. 1927. 



