104 LIBBIE H. HYMAN 



4. Young animals are invariably more susceptible to cyanide 

 than old ones. 



5. The CO2 production of pieces or animals runs parallel with 

 their susceptibility to cyanide, i.e., those more susceptible to 

 cyanide .show also a more rapid CO2 production. The CO2 

 production was determined by Dr. Tashiro with his very ingeni- 

 ous apparatus for measuring minute amounts of carbon dioxide 

 (Tashiro, '13). 



According, then, to the facts here presented, the time of death 

 in cyanide bears a direct relation to the previous rate of metab- 

 olism. Individuals or parts with the highest rate of metabolism 

 die first, those with the lowest rate last, and the others at inter- 

 mediate times; the cause of this, as already stated, is to be sought 

 in the asphyxiating action of the cyanides, as a result of which 

 the time of death of each part is proportional to its rate of oxy- 

 gen consumption. It is only necessary that the death point 

 should be clearly indicated to the observer; this is brought about 

 in the lower invertebrates through the disintegration which 

 promptly follows death. As a check on one's observations, one 

 may remove the animal or piece at any stage of the disintegration 

 to water, whereupon recovery of the intact parts takes place. 

 In this way, I have satisfied myself that disintegration follows 

 death almost instantly. The cyanide method is, of course, not 

 applicable to forms in which, owing to resistant outer structures, 

 disintegration cannot occur; but even in such forms, the death 

 of the animal as a whole may usually be determined by employing 

 some other criterion of the death point. 



The technique of the cyanide method is simple. A concen- 

 tration of potassium cyanide sufficient to kill the animals within 

 one to three hours is used. This concentration must be deter- 

 mined for each species by preliminary experiments. For the 

 oligochaetes it varies from /o to yrro normal. The cyanide solu- 

 tion is made up fresh by weight for each experiment. Animals 

 or pieces which are to be compared as to susceptibility must have 

 been kept under the same conditions of food, temperature, etc., 

 previous to the experiment, and must be of approximately the 

 same size, unless size differences are the object of the experiment. 



