STUDY OF FERTILIZATION 425 



the membrane remains close to the egg ; the higher the 



alkahnity the more water is absorbed and the farther out 



is the membrane pushed. 



Relative Extrusion 

 Ph. of Membrane. 



9-2 .... . 121 



7-6 (normal) ... 100 



7-3 44 



6-9 16 



It seems tolerably clear, therefore, that the extrusion of 

 the fertilization membrane is due to the existence of an osmoti- 

 cally active electro-negative colloid between the egg-surface 

 and the fertilization membrane. 



The origin of the fertilization membrane and of the enclosed 

 colloid is, however, more difficult to determine. 



The relative impermeability of the unfertilized egg to water 

 and to all substances not soluble in oils or fats leads to the 

 suggestion that, like the protoplasmic surfaces of many cells, 

 the vitelline membrane contains a continuous lipoid phase. 

 Such a conclusion cannot be substantiated by direct experi- 

 mental evidence, but, if it be correct, then many facts receive 

 a reasonable explanation. It is, of course, well known that 

 the formation of the fertilization membrane can be brought 

 about by a great variety of artificial agents. Of these, the 

 simplest and most efficient are saponin, benzol, fatty acids, 

 esters, and soaps. All these substances are essen- 

 tially emulsifying agents for a lipoid surface in 

 contact with water. -^ 



Since the use of fatty acids is most commonly adopted as 

 a means of artificial membrane formation, it is interesting to 

 analyse their action in detail. The process is as follows : 



(i) Unfertilized eggs are placed in 50 c.c. sea-water+1-5 c.c. 



N/10 Butyric Acid for 1| mins. 

 (ii) They are then transferred to sea-water, containing 



a minimum concentration of hydroxyl ions. 



' And for this reason these substances in higher concentrations destroy 

 the normal protoplasmic surface of most cells : in other words, they are 

 also ' cytolytic ' agents. 



