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. 1 
. .. . Hence this supports Loeb’s view that membrane formation is 
induced by the liquefaction of the lipoids. 
(I had previously referred the formation of the fertilization 
membrane to a liquefaction of the lipoid on the surface of the 
egg.”) 
We will now examine more closely the experiments upon 
which von Knaffi 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 flowimg together into 
1 Von Knaffl, op. cit. 
2 Loeb, ‘‘Ueber den chemischen Charakter des Befruchtungsvorgangs,”’ 
Rouz’s Abhandlungen und Vortrdge, Leipzig, 1908. 
