190 C. M. CHILD 



fact, these results correspond to those obtained by the indirect 

 method with alcohol and KCN: there is no doubt that a certain 

 amount of acclimatization occurs in Lot A 1 of this series. At 

 22.15 hours the three worms of Lot A 1 which were still intact 

 showed some slight recovery from the complete narcosis of the 

 preceding day. In other words, this concentration of benzamid 

 gives us indirect results in which the acclimatization factor is 

 involved, consequently here the resistance of the worms varies 

 directly as the rate of reaction. 



These two series are sufficient to show that the coefficient of 

 distribution of benzamid is of little importance in determining 

 the narcotic effect on Planaria and the resistance of the animals 

 to it. Here as in the case of alcohol, the rate of reaction is the 

 most important factor. It must not be forgotten, however, 

 that in the vertebrates with the great volume of lipoids in the 

 nervous system the coefficient of distribution of a narcotic may 

 be a much more important factor in determining its physiological 

 effect. But there as elsewhere, this factor remains a condition, 

 not a cause. 



4. The evidence from animals of different age 



When young and old animals are compared by the direct method 

 the resistance of the young animals is always much lower than 

 that of the old. This method has been used with both KCN 

 and alcohol on Planaria dorotocephala and with KCN on P. 

 maculata, P. velata, Phagocata gracilis, Mesostomum sp. and 

 embryonic and larval stages of Amblystoma. In all cases the 

 same result was obtained, the younger animals died and disinte- 

 grated earlier than the older. In the cases of Planaria doroto- 

 cephala and P. velata both the younger and older animals were 

 undoubtedly the products of asexual reproduction, as sexual 

 reproduction has not been observed in P. velata and only in a 

 single individual in P. dorotocephala during the years that I have 

 had these forms under observation. In Planaria maculata, on 

 the other hand, the young worms used in experiment were raised 

 directly from eggs laid in the laboratory and in the other forms 

 mentioned above asexual reproduction does not occur. As a 



