202 CM. CHILD 



rate of reaction with all the substances used indicates clearly a 

 certain similarity in the nature of their action. 



Moreover, the effects of alcohol, ether and chloretone upon 

 morphogenesis are in their essential features similar to those pro- 

 duced by KCN and on the other hand to those produced by low 

 temperature, products of metabolism in the water, etc. (Child 

 '11 c '11 d). Evidently all these substances act in some way to 

 decrease the rate of 'the metabolic processes. Similar conclu- 

 sions have been reached by various authors and on the bases of 

 various lines of investigation. The similarity in the effects of 

 KCN and alcohol, ether, etc., suggests that all act in some way 

 on the oxidation processes. 



But that the action of the alcohol is not the same as that of the 

 cyanides is clearly indicated by the difference in the capacity 

 for acclimatization to the two substances. Alcohol 4 per cent 

 kills the worms within a few hours, but in alcohol 1 per cent most 

 worms become acclimated. KCN 0.001 m. kills the worms in 

 about the same time as alcohol 4 per cent, but no appreciable 

 degree of acclimatization occurs in concentrations higher than 

 0.00004 m. To what is this difference due? 



The planarian is exceptionally good material in many ways 

 for determining the physiological effect of chemical substances, 

 andparticularly for purposes of comparison of different substances. 

 In many cases also two different aspects, the physiological and 

 the morphological, of the effect may be compared with each other: 

 this possibility in turn gives us a method of attack on certain 

 morphological problems which have scarcely been accessible 

 heretofore. 



The results of the experiments with depressing agents on Pla- 

 naria have an important bearing on the geiieral theory of narcosis 

 for they indicate very clearly that the coefficient of distribution 

 of the narcotic between water and fat has no necessary relation to 

 its narcotic action. In Planaria, where there is no great accumu- 

 lation of lipoids in any organ, we have seen that the coefficient 

 of distribution is a factor of very little importance as compared 

 with the rate of reaction in the organism. But attention has 

 already been called to the point that in the vertebrates, where the 



