158 C. M. CHILD 



resistance, rate of reaction and concentration of reagent are 

 briefly as follows: 



1. In relatively high concentrations in which the maximum length 

 of life is only a few houra, the length of life or resistance varies 

 inversely as the rate of reaction: the higher the rate, the earlier death 

 and disintegration occur and vice versa. This form of the method 

 which requires relatively high concentrations, I have called the 

 'direct resistance' method. 



2. In relatively low concentrations in which the animals remain 

 alive for days or weeks and in which some degree of acclimatization 

 occurs the length of life or resistance varies directly with the rate of 

 reaction except ^?^ certain cases where incidental factors modify the 

 result: the higher the rate, the more complete the acclimatization 

 and the greater the length of life. This form of the method which 

 requires low concentrations and long times and which determines 

 the resistance indirectly through the degree of acclimatization, 

 I have called the 'indirect resistance' method. 



3. Between these two extremes of concentration of the reagent 

 the results vary in character with the concentration and the rate 

 of reaction. For any two different rates of reaction it is possible 

 to find a concentration of the reagent in which the resistance will 

 be approximately the same : above this concentration the relation 

 is that of the direct method, below, it is that of the indirect 

 method. 



These conclusions are drawn from thousands of experiments 

 with alcohol and KCN by both the direct and the indirect methods. 

 Ether and chloretone have been used to a sufficient extent to 

 show that with them the relations are essentially the same. 

 Undoubtedly there are many other reagents particularly the 

 anesthetics, which would give similar results, but since I have 

 been primarily concerned with certain other problems, I have not 

 as yet taken the time to test any large number of anesthetics 

 or other substances with respect to this point. Of the different 

 substances used, KCN has proved to be the most satisfactory. 

 The differences in rate of reaction appear more clearly in most 

 cases in KCN than in alcohol or other anesthetics and the con- 

 centrations used are so low that various incidental factors are 



