ON CYANOGENESIS IN PLANTS. 
401 
distilled at first alone, and afterwards with the addition of dilute hydrochloric acid ; 
in the former case none, but in the second, where hydrolysis had occurred, con¬ 
siderable quantities of hydrocyanic acid were found in the distillate. 
These observations led us to conclude that Sorghum vulgare contains a glucoside 
which under the influence of some hydrolytic agent simultaneously present under¬ 
goes hydrolysis, furnishing as one product hydrocyanic acid, to which the observed 
toxicity of the young plants must be ascribed. 
A determination of the amount of acid which the air-dried plant is capable of 
producing at different stages of growth was made by leaving a weighed quantity 
in contact with water for 12 hours, and distilling off the acid formed in a slow 
current of steam, the liquid being titrated by LiebicLs method. 
The following results were obtained ;— 
C5 
( а ) From bright green plants about 12 inches in height; 
20 grammes gave a distillate requiring 7 ‘45 cub. centims. ' silver nitrate, 
equivalent to ’201 per cent. HON. 
1ST 
20 grammes gave a distillate requiring 7‘8 cub. centims. —- silver nitrate, 
equivalent to ‘216 per cent. HON. 
(б) From plants about 3 feet high, yellowish-green and ripe; 20 grammes of 
these mature plants gave no indication of prussic acid, and larger quantities on 
distillation with water gave amounts too small to be satisfactorily estimated. No 
prussic acid was obtained from the seeds of the Millet. 
It has Jbeen asserted by Greshoff and Treub that in many tropical plants 
hydrocyanic acid occurs as such, that is, in the free state. The existence of the 
free acid was demonstrated by these observers by immersing a thin section of the 
plant first in alkali, then in a mixture of ferrous and ferric chlorides, and finally in 
strong hydrochloric acid. If the plant tissue was stained blue, it was concluded that 
prussic acid in the free state was present. This test, however, appears to us to he 
quite inconclusive, as the mere moistening of plant tissue containing Loth a glucoside 
capable of furnishing prussic acid on hydrolysis and a hydrolytic enzyme, leads to 
the immediate production of free acid, which by Greshoff and Treub’s method 
would be regarded as occurring pre-formed in the plant. We have carefully 
examined various specimens of dhurra for free prussic acid by the following methods. 
About 20 grammes of the finely-powdered plant were placed in a distilling flask 
attached by its branch tube to a long condenser. Into the closed flask a rapid 
current of steam was passed, which served the double purpose of immediately 
destroying any enzyme, and of carrying through the condenser any volatile product 
present in the plant. In the distillate of the plant thus obtained we never found 
prussic acid, either with young Sorghum vulgare or Lotus arabicus. 
It therefore appears that, like Lotus arabicus , the poisonous effects of the young 
VOL. cxcix.— a. 3 F 
