574 



Dr. A. D. Waller. New Method for the [June 17, 



But, as stated above, the experiments, though striking in their results, 

 were rather of a domestic character than of physical precision. However 

 this may be, the difference between ordinary and " caffeine-free " coffee 

 affords a further proof that the toxic effect is principally due to the presence 

 of the caffeine. 



A New Method for the Quantitative Estimation of Hydrocyanic 

 Acid in Vegetable and Animal Tissues. 

 By Dr. A. D. Waller, F.E.S. 



(Received June 17, — Read June 30, 1910.) 

 (From the Physiological Laboratory of the University of London, South Kensington.) 



The evolution of hydrocyanic acid by laurel leaves (Frunus laurocerasus) 

 in consequence of congelation, or of their exposure to the action of anaesthetic 

 vapours, was first pointed out by Raphael Dubois.* It has been studied 

 more recently by Guignard,t who has introduced an extremely delicate test 

 for the presence of hydrocyanic acid by sodium picrate paper, and quite 

 recently this test has been applied by F. E. Armstrong! for the rapid detection 

 of ferments of the emulsin class. The reaction was first studied by 

 Hlasiwetz§ in 1859, who gave the following equation : — 



CeHaWT + SKCN-f 3H2O = C8H4KN5O6 + CO2 + NH3 + 2KH0. 



, ; 



Potassium isopurpurate. 



The reaction appeared likely to afford a convenient instance for the 

 simultaneous observation of chemical and electrical changes taking place in 

 living protoplasm under the influence of anaesthetics, and the immediate 

 purpose of this investigation was to determine the parallelism or the want 

 of parallelism between the course of the two changes — chemical and 

 electrical. 



Qualitative experiments in which the evolution of hydrocyanic acid from 

 laurel leaves was followed by means of picrate paper, the leaves being 

 enclosed in corked tubes containing the vapouV of (1) chloroform ; (2) ether; 

 (3) alcohol; and (4) water, gave results in tlie older of intensity (1), (2), (3), 



* R. Duboifl, ' Richet'H J)ictionaire de DiyHiologio,' art. " Hydratation." 

 t Guignard, ' linllotin des Sciences Pliarnia<!ologi(nioa,' 1900, p. 41.'). 

 I E. F. ArniHtrong, ' rhyaiol. Hoc. Proc.,' Miirrh 1!), 1910. 

 S HlaHiwotz, ]>iebig'H ' Amialen,' vol. 110, p. 2H9, 18,5!). 



