736 PATTERNS AND PROBLEMS OF DEVELOPMENT 



seded by other methods, but it should not be forgotten that it represented one of the 

 pioneer methods in the field. Later CO2 estimations were made colorimetrically (Child, 

 igigb, c; Robbins and Child, 1920). Differential susceptibiHty to lack of oxygen was 

 found to parallel cyanide susceptibility in the forms tested. Comparison of the data 

 appeared to indicate that differential susceptibility to KCN may serve as a rough 

 indicator of quantitative differences in respiratory or oxidative metabolism in many 

 organisms. The determinations by Hyman of the action of KCN on oxygen consump- 

 tion (Hyman, 191 6i; 1919a, e; 1920c) and on oxygen consumption in Dugesia, fed and 

 starved individuals (1919^, 1920(7), pieces and animals after reconstitution (1919c, 

 19236), and young and old individuals (i9i9(/) provided a more adequate basis for 

 comparison of respiration and susceptibility to KCN and further evidence of parallel 

 differentials and individual differences. 



Some of the results of these investigations and the conclusions drawn from them 

 aroused criticism of the hypothesis that differential susceptibility to cyanide might 

 indicate differentials in respiratory or oxidative metabolism. Certain of these criti- 

 cisms were due to misunderstanding. On the basis of his findings that oxygen con- 

 sumption is not decreased by KCN in starved Paramecium, even in gradually lethal 

 concentrations, E. J. Lund (1918a, b; 1921a) held that conclusions drawn from differ- 

 ential susceptibility were invalid, and B. L. Lund (1918) maintained that differences 

 in survival time in KCN of Paramecium and Didinium individuals of different age and 

 nutritive condition are due to differences in permeability. The criticisms are, in large 

 part, misdirected because based on the assumption that Child and Hyman had main- 

 tained that the toxic action of KCN is exerted only on the ectoplasm of Paramecium 

 and on the body wall only in planarians. No such view was ever advanced by these 

 authors. They merely pointed out that the susceptibility gradient observed in Para- 

 mecium occurred only in the ectoplasm and that the gradient in planarians could be 

 observed with certainty only in the body wall because the concentration of KCN 

 which reached the internal organs and the time when a lethal concentration reached 

 them might depend to some extent on the susceptibility and time of disintegration of 

 the body wall. That the internal organs of planarians were susceptible was shown 

 clearly enough by their complete disintegration and particularly by the much later 

 disintegration of the digestive tract in starved, than in fed, animals, as compared 

 with the body wall; but whether definite susceptibility gradients were present in the 

 gut or other internal organs, and, if so, whether they were in the same direction as the 

 gradient in the body wall, could not be determined with any certainty. 



Lund's conclusion that KCN has little or no effect on respiration in Paramecium has 

 been in part confirmed by later work on Colpidium (Pitts, 1931), in which a decrease 

 of 25 per cent was observed, and on Paramecium (Shoup and Boykin, 1931; Gerard 

 and Hyman, 1931), showing httle effect. According to earlier unpublished data 

 obtained by Hyman, which are mentioned here with her permission, a considerable 

 decrease in oxygen consumption of Paramecium sometimes occurs in KCN, but thus 

 far the factors which determine the occurrence or absence of decrease are not known. 

 In connection with this question it is important to note that the cyanide death gradi- 

 ent in Paramecium and other ciliates appears only in the ectoplasm. This, of course, 

 does not mean that the entoplasm is not susceptible to cyanide but only that it shows 

 no definite gradient, as might be expected, since it is in continuous circulation. It seems 



