1910.] Quantitative Estimation of Hydrocyanic Acid, etc. 



577 



applicable. On laurel leaves under the influence of anaesthetics, the daily 

 or hourly evolution of HON can be followed in a series of tubes from 

 which the contents are decanted at stated intervals (vide infra, figs. 2 

 and 3). On animals (and on man) the tenour in HCN in blood, or in other 

 tissues, can be quantitatively estimated by the colours of distillates from 

 known weights of material into suitable volumes of picrate (vide infra, 

 Experiments 1 to 25). 



As regards its application to the particular question stated above, as to the 

 parallelism between chemical and electrical phenomena in laurel leaves, it has 

 furnished what, in my judgment, is a clear and unmistakable answer, to the 

 effect that the evolution of hydrocyanic acid — so far from being a sign of 

 life in the sense that the electrical response is a sign of life — is a sign of loss 

 •of life, and, at any rate as to its main bulk, a post.-morte7n phenomenon. 



On the Time-Relations of Electrical and Chemical Changes taking Place in 



Ancesthetised Laurel Leaves. 



The earliest time after exposure to CHCI3 vapour at which an evolution of 

 HCN can be detected has, in my observation, been 5 minutes. The 

 electrical response to a strong induction shock, i.e. the ingoing homodrome 

 or antidrome blaze-current (which, as has been described at length elsewhere,* 

 is a characteristic sign of life), is completely abolished as early as one 

 minute after exposure to chloroform vapour. (Young tender leaves are 

 best adapted to this experiment. Older leaves, by reason of their high 

 ■electrical resistance, are not suitable.) 



We may not infer from the time-difference alone that the evolution of 

 HCN is a post-mortem phenomenon, since it may be due to " lag " in the 

 production and diffusion of HCN, and in the reaction of HCN with picric 

 acid. 



But a leaf which, after a minute's exposure to CHCI3 vapour, has lost 

 its electrical excitability, and which begins to give signs of HCN 10 minutes 

 later, and goes on giving olf HCN for hours and days is assuredly dead. 

 The HCN is then, in the main, a product of post-mortem action in a leaf 

 that was killed during the first minute. 



The following figures will be sufficient to illustrate the course of this post- 

 mortem fermentation, which, like other chemical actions, takes place more 

 rapidly at higher than at lower temperatures : — 



* Waller, ' Lectures on the Signs of Life,' 1903, p. 87 (§ 55), p. 94 (§ 59), p. 109 (§ 65). 



