186 C. M. CHILD 



primary effect ends and acclimatization begins, for both show the 

 same relation to temperature changes and one merges into the 

 other. 



But if we accept the above interpretation of the results obtained 

 with Planaria, how are we to interpret Meyer's results with tad- 

 poles, viz., that in temperature experiments the narcotic effect 

 varies with the coefficient of distribution. It is e\ddent that if 

 only minimal concentrations of the reagents are used, if the vol- 

 ume of lipoids in an organism or tissue is very great and if the 

 total volume of chemical reaction is relatively small, then the 

 coefficient of distribution may become the chief factor in deter- 

 mining the physiological effect of a narcotic. In the vertebrate 

 nervous system the volume of lipoids is very great and, except in 

 the earlier stages of development, the actual volume of chemical 

 reaction is small. Moreover, Meyer's results are for minimal 

 concentrations only. Undoubtedly the concentration of the nar- 

 cotic in the nervous system of the tadpoles is the chief factor in 

 determining the narcotic effect. It is at once apparent that this 

 is a case where the coefficient of distribution may be the determin- 

 ing factor, but it is also apparent that generalization on the basis 

 of this case alone can lead only to wrong conclusions. If Meyer 

 had worked with some of the lower invertebrates as well as with 

 the tadpoles and if he had used higher as well as minimal concen- 

 trations, he would have reached very different conclusions. 



My experiments permit only the conclusion that the action of 

 benzamid on Planaria is of essentially the same character as that 

 of alcohol, KCN, etc. In higher concentrations the resistance 

 of the animals varies inversely as the rate of reaction; in lower 

 concentrations it varies directly as the rate of reaction, except in 

 certain cases where incidental factors such as the coefficient of 

 distribution, nutritive condition, etc., play a part. Under the 

 usual conditions and in organisms where the differentiation of 

 tissues, and especially the accumulation of lipoids is not very great 

 the rate of reaction in the organism is by far the most important 

 factor in determining the resistance and the other factors become 

 practically negligible. In general then the experiments with 



