MEMBRANE CHANGES DURING STIMULATION 355 



increasing substances in general (equivalent to cytolytic 

 with long-continued action), whatever their special 

 chemical nature, have the same activating effect on sea- 

 urchin eggs.' The substances used included numerous 

 lipoid-solvent organic compounds, acids, bases, soaps, 

 alkaloids, cytolytic glucosides (saponin, etc.), and 

 foreign blood sera. A brief or superficial cytolytic 

 action is thus regarded by Loeb as the initial or critical 

 change in activation. This use of the term "cytolytic" 

 seems, however, to be open to objection, since, as usually 

 employed, it implies an irreversible or destructive 

 effect on the cell; whereas the primary or critical change 

 produced in activation is apparently a brief temporary 

 increase of surface-permeability resulting from a rapidly 

 reversed breakdown of the protoplasmic surface layer. 

 The connection between this effect and activation is 

 undoubtedly highly indirect and complex; but the same 

 may be said for the connection between the direct action 

 of any stimulating agent on an irritable tissue and the 

 succeeding response of the latter. What is significant 

 is that in both cases the primary or initiatory change in 

 the complex physiological sequence appears to consist 

 in a temporary disruption or breakdown (an effect 

 probably related to de-emulsification) of the protoplasmic 

 surface layer. This change furnishes the releasing 

 condition for those metabolic and other processes of 

 which the characteristic vital ''response" is the eventual 

 and biologically important consequence or expression. 

 Physical agents like ultra-violet radiation or heat 

 (30-40°), which also cause cytolysis in unfertilized eggs 



^ Artificial Parthenogenesis and Fertilization, University of Chicago 

 Press (1913). 



