THE AXIAL GRADIENTS IN HYDROZOA. 2 19 



plasmic substance, the total metabolism begins to increase, and 

 sooner or later attains a higher level than in the original animal. 

 During this period susceptibility of both body wall and alimentary 

 tract increases, but the susceptibility of the latter always remains 

 lower as compared with that of the body wall in the starved 

 than in the fed animal. 



The apparent discrepancy between the susceptibility and meta- 

 bolic methods results simply from the fact that the alimentary 

 tract, and doubtless the entoplasm in Paramecium soon becomes 

 practically inactive functionally in starvation while the body wall 

 does not. Consequently total metabolism may decrease while 

 susceptibility of the body wall increases or remains unchanged, 

 but later both the susceptibility of body-wall and alimentary 

 tract and the total metabolism increase. 1 



This discussion is sufficient to make it at least highly probable 

 that Lund's conclusions result rather from inadequate analysis 

 of his own experimental data in the light of the known facts, than 

 from any real discrepancy between the results obtained by the 

 susceptibility method and by direct measure of oxidation. He 

 has failed to take account of two very essential facts: first, that 

 ectoplasmic or body-wall oxidation is very far from being total 

 oxidation and second that the rate of oxidation in ectoplasm and 

 entoplasm or in body-wall and alimentary tract may vary inde- 

 pendently, that of the alimentary tract or the entoplasm under- 

 going marked decrease in starvation. 



Attention must also be called to the fact that the susceptibility 

 method does not, as Lund asserts, depend upon the assumption 

 that cyanide is a specific inhibitor of oxidations, for the regional 

 differences in susceptibility, the susceptibility gradients as well 

 as the differences with age and other conditions, are the same 

 with many other chemical and physical agents and conditions 

 in proper concentration or intensity, including for example high 

 and low temperatures and lack of oxygen and perhaps external 

 agents and conditions in general, as they are with cyanide. 



The anesthetics and dyes used in the study of susceptibility in 

 hydra, for example, give the same results as cyanide except where 



1 Lund was also informed in personal correspondence concerning our results on 

 Planaria and the reason for the apparent discrepancy between susceptibility and 

 total metabolism was pointed out to him. 



