Sovie Physical Properties of Protoplasm 257 



The mechanism of protoplasmic movement in shme molds is, 

 then, one of rhythmic contraction and relaxation of the plasmodium, 

 with a total of 95 seconds for each pulsation, 45 seconds for systole 

 and 50 seconds for diastole, the additional 5 seconds in time of out- 

 ward flow account for advancement. Kamiya (p. 211) gives 93.7 

 seconds for one rhythmic period. 



The precise nature of protoplasmic contractility is difficult of 

 interpretation, for in slime molds it is complicated by the constantly 

 varying shape of the plasmodium, and by a multiplicity of rhythms 

 (see Kamiya, p. 234). The latter are the expression of a too little 

 appreciated property of non-cellular protoplasm, namely, the pres- 

 ence of distinct regions, each with its own individuality, yet each 

 contributing to the function of the whole. Moving pictures revealed 

 three separate rhythms in slime (Figs. 14 to 17) , which number 

 Kamiya has now greatly increased. He postulates many rhythms 

 or frequencies of pulsations. 



The discovery that a plasmodium is a polyrhythmic system would 

 at first thought seem to hopelessly complicate the situation, but 

 actually it is only through a multiplicity of secondary pulsations 

 that it is possible to account for a number of phenomena. Where the 

 situation is a simple one, it is not difficult to visualize the mechanism 

 responsible for protoplasmic flow. If there is a strand connecting 

 two masses of protoplasm, then the mass at one end contracts and 

 that at the other end expands, forcing the protoplasm through the 

 connecting strand. At the end of 45 seconds the second mass under- 

 goes contraction and the first mass now expands. The protoplasm 

 then flows in the opposite direction for an average of 50 seconds. 

 It is probable that in such a case contraction takes the form of a 

 peristaltic wave which passes along the strand from one end to the 

 other, and then returns, the process being repeated rhythmically 

 every three-quarters of a minute. 



In a situation such as the foregoing, the outer cortical layer of 

 the protoplasm may be postulated as the region responsible for con- 

 tractility and protoplasmic flow; and, with reason, it may be assumed 

 that this surface layer is a gel, in contrast to the fluid protoplasm 

 which is in a state of motion within, the one being readily converted 

 into the other through a sol-gel transformation. Though in full agree- 

 ment with this viewpoint where there is one general inner region 

 of liquid and flowing endoplasm, surrounded by an outer firm and 

 contractile ectoplasm, as in Amoeba, yet I do not believe so simple 



