TIIIRTEBN FIGURES
Many investigations have been made of the effect of cyanide on living cells and tissues, but certain phases of cyanide action a r e still not clearly understood. This study is a continuation of the research on the action of cyanide on the egg and embryo of the grasshopper, which has been conducted at this laboratory β¬or several years (Roblnie, Boell and Bodine, '38; etc.). F o r general reviews of the subject of cellular oxidation and cyanide inhibition, the reader is referred to the recent publications of Commoner ('40), Oppenlieiiner and Stern ('39), and Barron I n all of the experiments described, certain precautions regarding neutralization, evaporation, HCN equilibrium between the experimental fluid and tbc center well solutions, etc., discussed by Bodine and Robbie ('41), were observed. Since KCN neutralized by HCl is almost entirely in the form of HCN, the latter term is used rather than the former.
IJnless otherwise noted all determinations and exposures were made a t 25Β°C.
( '39).
THE RATE O F ACTION O F HCN
Cyanide is believed to exert its depressing action on cellular respiration by combining with the oxygen transport systems within the cell, possibly the cytochrome-cytochrome oxidase system of Warburg and Keilin. It has been generally believed that the inhibiting action of cyanide is upon the enzyme cytochrome oxidase, but Potter ('41), on thc basis of spectrophotometric observations of various animal tissues, suggests that it may be cytochrome c that is the locus of cyanide action rather than the oxidase.
I n the grasshopper egg the time required for maximum depression and the level of uninhibited respiration a r e dependent upon the concentration of HCN. This is illustrated in figure 1. In the experiment represented groups of fifty postdiapanse eggs were placed i n Warburg * dided by a grant from the Rockefeller Foundation f o r research in cellular physiology.