136 RALPH S. LILLIE. 



position of two effects, one a structural alteration due directly 

 to high temperature, the other a chemical combination of the 

 acid with some cell-constituent. The second is the critical 

 event in activation, but its rate is determined not only by the 

 temperature but by the structural conditions in the egg-system. 

 The action of butyric acid at 6 and lower also represents a 

 summation of two activating influences, cold and acid. I shall 

 deal with this case separately, and shall consider first the tem- 

 perature-coefficients of the action of butyric acid between 8 

 and 28, temperatures which by themselves have no activating 

 effect. 



(a) Experiments with Butyric Acid Solution at 8 to 28. 



It was shown in my two preceding papers 1 that the degree of 

 activation (as indicated by the proportion of favorably developing 

 eggs) resulting from exposure to a given solution of butyric acid 

 at ordinary temperatures increases with increasing time of ex- 

 posure up to an optimum. Exposures longer than this optimum 

 are injurious and beyond a certain maximum simply cause 

 cytolysis without activation. This rule holds for the action of 

 butyric acid at all temperatures. The interval between the 

 minimum for visible activation (membrane-formation alone) 

 and the optimum decreases rapidly as temperature rises; at 8 

 this interval is approximately forty minutes, at 18 six to eight 

 minutes, and at 28 less than one minute. A curve relating 

 degree of activation (the percentage of eggs forming blastulae) to 

 time of exposure may thus be constructed for each temperature. 

 The form of this curve appears to be the same at all temperatures, 

 although as just indicated the time-range which it occupies is 

 shorter at higher temperatures. This behavior is consistent with 

 the foregoing hypothesis that activation depends upon the pro- 

 gressive formation of a reaction-product (acid plus egg-substance 

 = activating-substance) to a critical local concentration or 

 quantity, the rate of formation being a function of temperature 

 and concentration of acid. 



According to this hypothesis, the interval between the be- 

 ginning of exposure and the optimum ought to vary with tem- 



1 Loc. cit. 



