94 C. M. CHILD 



Alcohol and acids act as inhibiting agents in sufficiently high 

 concentration, but are less effective in producing differential 

 inhibitions of development than any other agents used, because 

 in almost any concentrations which do not actually kill, accli- 

 mation begins within a very short time, and, by the time devel- 

 opment has reached the limit determined by the conditions of ex- 

 periment, the primary differential inhibition is compensated or 

 in most cases over-compensated to a high degree by differential 

 acclimation. Acclimation to acids occurs even more rapidly 

 and to a greater extent than to alcohol. Consequently, with 

 alcohol and acids, the more extreme types of differential inhi- 

 bition are best obtained by the action of high concentrations, 

 beginning at the blastula or gastrula stage instead of at the be- 

 ginning of development, for this procedure leaves little time for 

 the occurrence of acclimation. Alcohol and acids, acting from 

 the beginning of development, are the most effective of all 

 agents used in producing the more extreme types of differential 

 acclimation, and the acids are somewhat more effective than 

 alcohol. The differential effects of recovery after the tempo- 

 rary action of alcohol are, like those of KCN, similar in charac- 

 ter to the differential effects of acclimation and there is every 

 reason to believe that the same is true of acids. 



It is evident from these facts that the different reagents used 

 may be arranged in a series according to their differential effects 

 on development and larval forms. The agents which are most 

 effective in producing the differentially inhibited types of form 

 are least effective in producing the types of form characteristic 

 of differential acclimation, and vice versa, and between the ex- 

 tremes of KCN' and acids, NH 4 OH, NaOH and alcohol may be 

 placed in the order given. So far as the observations go, the 

 relations as regards differential recovery after temporary action 

 are the same as for differential acclimation. These differences 

 in action of different agents depend upon the rapidity and de- 

 gree of reversibility of their effects on protoplasm with either 

 continuous or temporary action. I am inclined to believe that 

 these differences in effect upon development form and propor- 

 tions may be regarded as constituting to some extent a cri- 



