PHYSIOLOGICAL GRADIENTS. 155 



fore be regarded as to some extent a comparative measure or in- 

 dicator of rate of oxidation in the parts, organs or individuals 

 of a particular species. 1 



Comparison of the data on susceptibility with data obtained by 

 other methods has shown that a general non-specific relation 

 between susceptibility and physiological condition exists, at least 

 in the simple organisms and early developmental stages, where 

 the differentiation of organs is not so far advanced that a more 

 or less specific action of particular agents or particular organs 

 is involved. This relation is as follows : to a certain range of 

 concentrations or intensities of the agents used, which is experi- 

 mentally determined to be above the limit of acclimation or 

 tolerance for the particular species examined, susceptibility varies 



1 For the literature on the action of cyanide see Hyman, '19. Allen, '190, 

 and Hyman, '19, have shown that KNC greatly decreases oxygen consumption 

 in Planaria. I have found that KNC decreases CO 2 production in Planaria, 

 though apparently less than it decreases oxygen consumption and that KNC 

 and lack of oxygen are to some extent additive in their action on CO 2 produc- 

 tion (Child, 'igc). Lund claims that KNC does not decrease oxygen consump- 

 tion in Paramcccium (Lund, '18), tut it may be pointed out that the concen- 

 trations of KNC in his experiments give a solution of very high alkalinity 

 which produces extreme stimulation with intense motor activity often con- 

 tinuing for several hours until the inhibiting action of the cyanide appears. 

 With cyanide solutions brought almost or quite to neutrality there is no 

 apparent stimulation and no increase in motor activity. Lund did not neu- 

 tralize his KNC solutions, therefore the total oxygen consumption undoubtedly 

 does not represent the action of cyanide alone, but includes the stimulating 

 effect of the alkali. Repetition of the experiments in cyanide solutions with 

 H ion concentration approximately that of the normal environment of Para- 

 mcccium is of course necessary before final conclusions are possible, and a 

 repetition will be undertaken in this laboratory as soon as opportunity permits. 



More recently Lund ('20) has shown that KNC and lack of oxygen do not 

 act in the same way upon Planaria since with lack of oxygen CO 2 production 

 is not decreased during the period of the experiment, while it is decreased by 

 KNC. The method of CO 2 determination used by Lund is, as he has shown 

 (Lund, '19), not very accurate, but leaving out of account the possibility of 

 technical error, the work of various investigators indicates very clearly that 

 the effect of cyanides on protoplasm is not identical with the effect of lack of 

 oxygen. I have pointed out that cyanide and lack of oxygen are to some 

 extent additive in their action and that their action must therefore be similar 

 or identical in certain respects. Up to the present, therefore, Lund's work 

 affords no grounds for modifying the conclusions reached by earlier investi- 

 gators concerning the action of cyanide, and we are still justified in believing 

 that susceptibility to cyanides is in a general way and to some extent a measure 

 or an indicator of rate of oxidation. 



