II CLEAVAGE 43 



but to which the membrane is impermeable (Mammalian 

 blood- serum, for instance), the membrane at once collapses. 

 Should the lipoid-soluble reagent be allowed to penetrate still 

 further into the egg, the deeper parts of the latter become 

 liquefied and cytolysis occurs. 



It is, however, doubtful whether this hypothesis is entirely 

 satisfactory. Solution is a physical process, but the magni- 

 tude of the temperature coefficient or quotient points to a 

 chemical reaction, as Harvey and indeed Loeb himself have 

 shown. 



The temperature quotient for an interval of 10C. for 

 a chemical reaction is at least 2 : for a physical action it is 

 much lower. 



The following table shows that its magnitude for this 

 reaction is about 2 (taken from Harvey, for various Sea- 

 urchins). 



TABLE V. 



Optimum concentration 



Exposure in in C ' C ' f 15 aCetic to 



minutes. Temperature. 50 c.c. sea-water. 



H 23 6 



1$ 33 2-3 



3" 23 3-4 



3 33 l|-2 



6 23 3 



6 33 H 



The solution of the lipoids by the fatty acid must then be 

 rejected. A change in the surface-tension of the egg might 

 be suggested, but surface-tension is not altered much by 

 temperature, nor is the rate of diffusion, nor the dissociation 

 of the fatty acid. 



A chemical explanation is therefore put forward, namely, 

 that the acid combines with the protein at the egg-surface, 

 and that the compound so formed is more permeable than the 

 cytoplasm of the unfertilized egg. It is supposed then that 

 substances (protein) pass out through this surface-layer and 

 are immediately coagulated by the water to form the mem- 

 brane. Or else it may be imagined that the altered surface- 

 layer itself becomes the membrane. Through this membrane 



