OXYGEN CONSUMPTION IN THE PRESENCE OF CYANIDE. 405 



written, two additional papers have come to my attention, 

 those of Allen ('19) and of Evans ('19). Allen's results and 

 conclusions regarding the effect of potassium cyanide on the 

 rate of oxygen consumption of Planaria are about the same as 

 my own, except for one or two points; thus Allen states that the 

 oxygen consumption of Planaria cannot be reduced to less than 

 20 per cent, of the normal by cyanide, while I found in many 

 cases, reduction to 10 to 15 per cent, of the normal. Evans's 

 interesting paper contains some further references to the litera- 

 ture, confirms some previous work, and presents a number of 

 new facts. Thus Evans finds that cyanide decreases markedly 

 and reversibly the oxygen consumption of the cat, confirms the 

 older statements that oxygen is just as readily dissociable from 

 the blood in cyanide poisoning as from normal blood; and shows 

 a striking similarity between the behavior of smooth, skeletal, 

 and heart muscle, and nerve and nervous centers in the presence 

 of cyanide and in lack of oxygen. Evans concludes that the 

 cyanides "appear to exert all of their physiological effects by 

 reason of the anoxaemia which they produce," and favors the 

 view that they act by uniting chemically with some tissue con- 

 stituent. 1 



1 Comment would seem to be required on Evans's remark (p. 23) that the 

 observations of Lund and Herwerden seem to be incompatible with Child's con- 

 ception of metabolic gradients. Lund's results have been considered elsewhere 

 (Child, '19). Herwerden ('18) says that the buds and young of Hydra are not more 

 susceptible to cyanide than the parents. Perusal of her paper shows, however, 

 that she has compared only three or four pairs of individuals and has observed the 

 disintegration of the tentacles only, having removed the cyanide when this occurred. 

 Now, we have clearly shown (Child and Hyman, '19) that the buds of Hydra are 

 not comparable with the parents until they have the same degree of muscular activity, 

 and further that the susceptibility of the tentacles is also dependent upon their 

 degree of activity. Miss Herwerden is mistaken in her conclusion. We have com- 

 pared dozens of young and adult Hydras, belonging to three species, and have 

 always found that the young are more susceptible to cyanide when comparable 

 degrees of muscular activity exist. It is true that the difference is least in the case 

 of the tentacles but even there the tentacles of the young are slightly more sus- 

 ceptible. Neither are Miss Herwerden's statements about the susceptibility of the 

 Daphnid heart entirely correct. I have found that the smallest individuals in a 

 Daphnia culture are the most susceptible of all (both as to heart and entire animal) ; 

 that the susceptibility decreases with increasing size up through the size when the 

 females are producing their first parthenogenetic broods; but from that time on, 

 the relation is reversed, so that the largest and oldest individuals in the culture, 

 which have produced many parthenogenetic broods, are more susceptible than 



