ON CYANOGENESIS IN PLANTS. 
409 
hydrolysis by emulsin. It is the first member of the class of dextrose ethers 
(glucosides) of cyanhydrins which has so far been found in nature, amygdalin and 
lotusin being maltose derivatives. 
The Enzyme of Sorghum vulgare. 
In the introduction to this paper attention has been drawn to the fact that the 
plant when moistened with cold water evolves hydrocyanic acid, whilst it no longer 
does so after exposure to a temperature of 100°, nor is the acid formed when the 
plant is placed in boiling water. These results point to the presence in the plant of 
an enzyme, destroyed by heat, which has the power of hydrolysing dhurrin. This 
enzyme was isolated by extracting the finely-ground plant with cold water, and 
evaporating the extract so obtained in a vacuous desiccator over quicklime to remove 
as much hydrocyanic acid as possible. The activity of this extract was then tested 
by the addition of small quantities to solutions of amygdalin, salicin and dhurrin, 
these experiments being controlled by the addition of boiled and filtered dhurra 
extract to similar solutions of these glucosides. 
In all three cases the glucoside was quickly hydrolysed, the formation of benzalde- 
hyde, saligenin, and parahydroxybenzaldehyde respectively being recognized by the 
usual tests for these substances. Comparative experiments in which the action of an 
extract of sweet almonds was tried side by side with the dhurra enzyme on the same 
glucosides, showed that the two extracts behaved in precisely the same way. 
Similar preparations made by precipitating aqueous extracts of sweet almonds and 
dhurra with alcohol and by precipitating calcium phosphate in such extracts, showed 
no difference of activity in effecting the hydrolysis of salicin. The glucosidolytic 
enzyme of Sorghum vulgare therefore performs the same functions as the enzyme 
emulsin which occurs in sweet almonds, and in the present state of our knowledge 
of the chemistry of enzymes, the two substances may provisionally be regarded as 
identical. 
The Cyanogenetic Constituents of Plants. 
Besides lotusin and dhurrin, the glucosides we have isolated from young plants of 
Lotus arahicus and Sorghum vulgare respectively, only one other cyanogenetic 
glucoside is definitely known, that is, the amygdalin derived from bitter almonds, 
which, however, is found in the seeds of the plant. 
The results of our investigations have rendered it probable that the production of 
prussic acid in a number of other plants may be associated with the ijresence of 
cyanogenetic glucosides. Moreover, the question of the occurrence of prussic acid, 
and the part played by it in vegetable metabolism, involves problems of the first 
importance in vegetable physiology, with which we intend to deal when we have 
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