MEMBRANE FORMATION AND CYTOLYSIS 189 



The following conclusions reached by von Knaffl may be 

 mentioned by way of further explanation: 



Protoplasm is rich in lipoids; probably it is mainly an emulsion 

 of these and proteins. Any physical or chemical stimulus which can 

 liquefy the lipoids causes cytolysis of the egg. The protein of the egg 

 can really only swell or be dissolved if the condition of aggregation 

 of the lipoid is altered by chemical or physical agencies. The mechan- 

 ism of cytolysis consists in the liquefaction of the lipoids, and there- 

 upon the lipoid-free protein swells or is dissolved by taking up water. 

 .... Hence this supports Loeb's view that membrane formation is 

 induced by the liquefaction of the lipoids. 1 



(I had previously referred the formation of the fertilization 

 membrane to a liquefaction of the lipoid on the surface of the 

 egg. 2 ) 



We will now examine more closely the experiments upon 

 which von Knaffl based his view. When he heated the sea- 

 urchin egg to 41 C., cytolysis ensued: many strongly refracted 

 spherules appeared on the surface of the egg, as in Fig. 52. 

 He regards these globules as lipoids, since they disappear or 

 dissolve in the presence of benzol, chloroform, and alkali. 

 But they do not disappear in acetone, from which von Knaffl 

 concludes that they consist of lecithin. He regards the fact 

 that in cytolysis the egg can be observed to exude clear drops 

 which are soluble in benzol, as a support of the hypothesis 

 that membrane formation and cytolysis depend essentially 

 upon lipoids passing into solution, or being excreted from the 



egg. 



Now this exudation of lipoids may in reality explain the 



clarification of the egg that is characteristic of cytolysis. For 

 if the protoplasm consists of an emulsion in which the walls 

 of the vesicles are formed by a solid lipoid, a removal of these 

 walls must lead to many small vesicles flowing together into 



1 Von Knaffl, op. cit. 



2 Loeb, "Ueber den chemischen Charakter des Befruchtungsvorgangs," 



Roux's Abhandluii'ien and V'ortraye, Leipzig, 1908. 



