THE PROBLEM OF ACTIVATION 261 



measurable rate, which, however, varies with the kind 

 of eggs and with their condition, is well founded. Such 

 a change is not comparable to electrical depolarization 

 or decrease of surface tension. The rate at which the 

 cortical reaction spreads from the point of action of 

 the spermatozoon furnishes a new basis of judgment 

 concerning the probable nature of the change. The 

 general order of magnitude is of a physiological rather 

 than a purely physical sort. It is perhaps hardly neces- 

 sary to say that the activation of the egg at a given 

 point by the spermatozoon does not present a different 

 problem from artificial activation. It does, however, 

 give an additional point of view with reference to it. 



The primary change in activation is not something 

 visible in a morphological sense; the visible cortical 

 changes are due to activation and are obviously specific 

 for the kind of egg concerned; hence the considerable 

 variety that they exhibit in different animal groups. 

 Some theories of artificial activation have erred in 

 respect to undue emphasis on the morphological change 

 as though it were primary instead of being secondary 

 or even tertiary. The analysis implies, first, a physical 

 alteration at the point of fertilization; second, chemical 

 reaction in which a specific catalyzer is concerned; third, 

 the visible cortical effect. The writer is not fully con- 

 vinced that the chemical reactions may not be set up 

 directly, but this point is perhaps a minor one. 



Loeb (1910) has suggested that in the process of 

 cytolysis which he conceives to underly the activation 

 of the egg " certain substances which were solid are 

 liqufied and enabled to diffuse into the egg. If it 

 could be shown that these substances were of such a 



