234 PRUSSIC ACID IN THE LEGUMINOS^ 



prussic acid which occurs does not arise from a glucosidic 

 substance, reduced by an enzyme, but from a much less 

 stable combination. This is the conclusion reached by Dr. 

 Treub. " Besides, other experiments have demonstrated that 

 the reduction of the cyanhydric glucosides in the leaves may 

 be effected with remarkable rapidity. In direct distillations, 

 if cold water be poured over the leaves and these be im- 

 mediately heated, the quantity of prussic acid set free is much 

 larger than if boiling water had been used at the start. 

 Occasional! V the distillation even draws out the whole." 



Dr. Treub has carried his investigations still further and 

 has studied the formation of prussic acid, or rather of 

 cyanhydric glucoside, in plants. 



His researches on Phaseolus lunatus have furnished a 

 proof that the presence of a carbohydrate, and particularly 

 of dextrose, constitutes one of the indispensable conditions 

 of cyanogenesis in the leaves. Thus light merely acts as an 

 agent in the production of carbohydrates, which, in their 

 turn, are necessary for the formation of prussic acid. Cells 

 which normally produce prussic acid are equally capable of 

 forming it in darkness, provided the supply of carbohydrates 

 is sufficient. 



One method of proving this was that of enveloping wath 

 thin sheets of tin, either portions of young leaves (Pangium), 

 or the whole of the young leaves (Phaseolus). In spite of 

 etiolation, the foliaceous portions developed under these 

 conditions produced just as much prussic acid as normal 

 leaves. 



The researches we have quoted above are of considerable 

 interest and should prove of great assistance in the study 

 of Leguminosas containing prussic acid. At the same time 

 they are not the only ones which have been published on this 

 question. M. L. Guignard has devoted considerable attention 

 to plants containing prussic acid ; Messrs. Greshoff, Van 

 Romburgh, Henry, &c. ; and although these latter researches 

 are more general in character, the importance of the 



