BV JAMES -U. I'ETRIE. 



457 



the plant, t'yiiodon iHcompletus (blue touoli grass), when its enzyme was de- 

 stroyed by pouring on boiling water, and then distilled, yielded 35 % of its 

 hydrocyanic acid, although it was found subsequently that no free hydrocyanic 

 acid existed in this grass. Where plants were distilled, starting with cold water, 

 it has frequently been found that the whole of the hydrocyanic acid was evolved 

 within half an hour, although the enzjTne must have been destroyed at an early 

 stage . 



That the hydrocyanic acid obtained iu this way is not free acid in the plant 

 tissues was proved later iu Table D. The work of numerous investigators has 

 shown that enzyme action is very powerful during the tii-st few seconds, and it 

 is on this account almost impossible to destroy instantly the enzyme of leaves 

 by pouring ou boiling water. As the temperature of the mass rises the activity 

 of the enzyme is lapidly increased, and this increased activity acts in opposi- 

 tion to the destruction of the enzyme, until the latter by rise of temperature 

 overpowers it. At high temperatures, therefore, one may obsei-ve a great initial 

 velocity of enzyme action, and this, after a few seconds or minutes, comes to an 

 end. It is generally found that enzyme action is very incomplete at higher 

 temperatures. Dr. Treub, late Director of the Gardens of Buitenzorg, has 

 stated that this very rapid decomposition of the glucoside was of great physio- 

 logical importance, as at a sudden demand hydrocyanic acid could be liberated 

 and immediately utilised in the metabolism of the leaves. 



Direct distillation with acid gave varying figiires, the evolution of hydro- 

 cyanic acid ranging from 5 to 25 % of the possiljle amount. Some plants, such 

 as Sorghum, Poa flava, etc., when treated in this way yield the whole of their 

 hydrocyanic acid. 



The glucoside of Heterochndrvii is very incompletely hydrolysed by boiling 

 with dilute acids. 



T.\BLE B. — The plant, when autolysed for 1 day, and the glucoside decom- 

 posed by its own enzyme, liberated in sample i., 45 mgs. %, in samples ii. and iii. 

 120 mgs. %, and in sample iv. 38 mgs. %. Numbers i. and iv. are equivalent to 

 three fourths of the total hydrocyanic acid present, while ii. and iii. are only a 

 third. 



These experiments show that the leaves are deficient in enzyme. 



Some cyanogenetic plants such as Sorghum. Pruints spp., Paiiiciilaria spi»., 

 etc., yield much less hydrocyanic acid after maceration, and this method cannot be 

 used for the estimation. In these plants the greatest yield was obtained by direct 

 distillation with acid. 



Table C. — When the action of the natural enzyme of the plant is assisted by 

 adding eniulsin. the yield of free hydrocyanic acid is gi-eatly increased, the maxi- 

 mum amount obtained being 328 mg-s. %. 



In similar investigations, Guignard showed in the case of Sambucws nigra 

 (the elder), that the addition of emulsin before maceration gave no further in- 

 crease. ^'iehoever, and his colleagues, in America, found the same condition to 

 hold in tlieir experiments on Tridens flavus; and the writer has found that in 

 numerous other grasses an abundance of enzyme existed, sufficient to decompose 

 the whole of the glucoside. 



Treub's investigations show that emulsin of almonds has vei-y little action on 

 the cyanogenetic compounds of Phaseolus lunatiis, Pangium edule, Passiflora 

 fju-adranfjiilaris, Maiiihot, etc.; in certain other plants such as Sorghum, Hevea, 



