148 The Mechanistic Conception of Life 



droplet and the second phase of the emulsion. I assume that 

 only this stabilizing substance consists of lipoids, especially 

 cholesterin. The two other phases which constitute the 

 emulsion need not be lipoids. To fix our ideas provisionally 

 we may assume that these phases are first protein with little 

 water and second water with little protein. The existence of 

 these two phases has been established by Hardy. The emulsion 

 at the surface of the egg consists, according to this view, of a 

 system of protein droplets poor in water surrounded by a 

 stabilizing film of a lipoid (cholesterin or lecithin). If the sea- 

 urchin egg is treated with a lipoid solvent like benzol the 

 stabilizing film of cholesterin is dissolved and the protein drop- 

 let can absorb water. If we use saponin the film is destroyed 

 by the precipitation of cholesterin by saponin. The absorp- 

 tion of water leads to the lifting up of the surface film which 

 surrounds the egg.^ 



We wish to add a few remarks concerning the nature of this 

 surface film, although this does not belong to our problem. 

 According to Overton and Koeppe the surface film of cells 

 consists of lipoids, and according to Koeppe cytolysis is deter- 

 mined by the solution or tearing of this film. This view is not 

 tenable, since the surface film which is lifted off in the form of 

 the fertilization membrane does not consist of a lipoid but of 

 protein. This is suggested by the fact that this membrane is 

 absolutely insoluble in any lipoid solvent. Moreover, this 

 membrane remains perfectly intact when the egg is transformed 



into a ''ghost." 



X 



Since we can cause the formation of a membrane of fertili- 

 zation in the star-fish egg by gentle agitation or mere pressure, 



1 We have assumed here that the fertilization membrane is preformed in the 

 imfertilized egg and lifted up in consequence of the cytolysis of the layer beneath 

 it. As I stated in my book on Die chemische Entwicklungserregung des tierischen 

 Eies, it is also possible that the fertilization membrane is a membrane of precipita- 

 tion formed through the reaction of a constituent of the liquefied cortical layer 

 with a constituent of the sea-water (Ca?). It is immaterial for the problem 

 discussed in this paper which view we adopt temporarily. 



