APPENDIXES 737 



to be evident that there are oxidation systems in Paramecium httle or not at all affected 

 by cyanide, but the data on the death gradient in KCN and on the effect of KCN on 

 respiration are not comparable, because the former concern the ectoplasm only, the 

 latter the whole organism. It is still possible that cyanide may decrease respiration 

 in the ectoplasm of Paramecium; but, since the ectoplasm is, to a considerable extent, 

 differentiated into structural constituents, some of which may not respire actively, 

 the total ectoplasmic respiration may be only a small fraction of the total respiration, 

 and its decrease by cyanide may not be evident with the methods available. It is cer- 

 tain that the ectoplasmic gradient of differential dye reduction in low oxygen (Child, 

 19346) is the same as the susceptibility gradient to cyanide and to lack of oxygen. 



G. D. Allen (1919(7), Hyman (igigc), and Buchanan (19260) found that oxygen 

 consumption in Diigcsia is decreased by KCN, and Lund (1921/)) showed that it is also 

 decreased by decrease in oxygen concentration. Determinations of CO2 production in 

 pieces of D. agilis after certain starvation periods led Allen {igigb, 1920) to question the 

 data on differential susceptibility in D. dorotocephala and the inferences drawn from 

 them. It was shown by Hyman (1919/), 19200), however, that with a longer starvation 

 period than that in AUen's experiments the respiratory changes in D. agilis were 

 similar to those in D. dorotocephala. It was also found by Hyman (i9i9r, d; 19236) 

 that the differences in oxygen consumption in relation to reconstitution, physiological 

 age, and size and level of origin of piece were parallel to the observed differences in 

 susceptibility. Comparative colorimetric CO2 estimations showed differences in CO2 

 production parallel, in general, to the differences in oxygen consumption found by 

 Hyman; differential susceptibility to lack of oxygen was found to be parallel to the 

 cyanide differential; and it was shown that KCN and lack of oxygen are additive as 

 regards their effect on survival time (Child, i9i9(:). Robbins and Child (1920) showed 

 that differences in CO2 production, as colorimetrically estimated, paralleled the differ- 

 ences in oxygen consumption and susceptibility. The action of KCN on oxygen con- 

 sumption in various other invertebrates was also investigated (Hyman, 19166, 1919a, 

 e, igioc; Galigher, 19216; Allee, 1923); in all cases there was a decrease with the 

 higher concentrations, but in some forms a primary increase occurred with low con- 

 centrations. 



In planarians, as in Paramecium, data on susceptibility and on respiration are not 

 comparable in all respects. As noted above, observations on differential susceptibility 

 concern the body wall because susceptibility of internal organs cannot be determined 

 independently of that of the body wall. In well-fed animals the gut disintegrates as 

 early as, or even earlier than, the body wall; but after long starvation, later than the 

 body wall. This difference is suggestive of a considerable difference in physiological 

 condition between the actively functioning and the long-starved gut. Respiratory 

 determinations include gut and body wall and other internal organs. Pieces from 

 different body-levels of well-fed planarians usually do not show any consistent evi- 

 dence of a longitudinal respiratory gradient. In order to obtain evidence of this gradi- 

 ent, as well as in most other determinations of respiration, it has been found necessary 

 to keep the animals without food for at least a week or two before work with them, in 

 order that the digestive tract may be empty and quiescent. When starved animals are 

 fed, respiration increases very greatly. This brief survey of the question of cyanide 

 susceptibility in relation to respiration in Paramecium and planarians indicates that 



