448 Brenchley . — Organic Plant Poisons. /. 
animal body if they are utilized in very small quantities, and this knowledge 
has been made full use of by medical science. In some quarters the idea 
gradually evolved itself that all poisons behave as stimulants under 
favourable conditions, and it was assumed that this applied to plants as well 
as animals. In 1896 the position of affairs was thus summed up by 
Hiippe: 1 ‘Jeder Korper, der in bestimmter Concentration Protoplasma 
todtet und vernichtet, in geringeren Mengen die Entwickelungsfahigkeit 
aufhebt, aber in noch geringeren Mengen, jenseits eines Indififerenzpunktes, 
umgekehrt als Reiz wirkt und die Lebenseigenschaften erhoht.’ This 
theory has been frequently put to the test, especially with regard to metallic 
compounds, and the results indicate that it is by no means a universal law, 
but that while toxic compounds reach an indifferent point as the concentra- 
tion decreases, it does not always happen that stimulation occurs with still 
greater dilution. 2 There is less experimental evidence with regard to 
organic compounds, so during the last four years an attempt has been made 
at Rothamsted to gain further information with regard to some of the more 
common and economically interesting substances. 
Hydrocyanic Acid. 
This substance has possibly attracted more attention than any other 
plant constituent on account of its deadly poisonous nature and its 
presence in many articles used as food for man and animals. Numerous 
cases of poisoning by Soy beans {Phaseolus hmatus) and Sorghum 
(Sorghum vulgar e ) have occurred, and the economic importance of this 
fact has given an impetus to investigations on the subject. Prussic acid is 
formed by a goodly number of plants, representative of a variety of natural 
orders, of which Rosaceae furnishes a considerable number of instances. 
The presence of prussic acid in the oil of bitter almonds had long been 
known, but in 1830 Robiquet and Boutron Charlard 3 recognized that it did 
not really exist as such in the fruit, but that water was essential for its 
formation ; they realized that bitter almonds contained a principle — 
amygdalin — which under certain conditions gives rise to prussic acid. It 
has since been recognized that hydrocyanic acid as such rarely occurs in 
plants, but that it is evolved by the interaction of cyanogenetic glucosides 
(such as amygdalin) and enzymes (such as emulsin) in the presence of 
water. Usually these two essential principles are localized in the same 
plant or parts of plants, but in some cases one may be present without the 
other, when there is no formation of hydrocyanic acid unless the missing 
constituent is supplied in some way. Amygdalin was the first cyanogenetic 
1 Hiippe, F. : Naturwissenschaftliche Einfiihrung in die Bakteriologie. Wiesbaden, 1896. 
Quoted by Copeland, Bot. Gaz., 1903, vol. xxxv, p. 83. 
2 See Brenchley, W. E. : Inorganic Plant Poisons and Stimulants. Cambridge University 
Press, 1914. 
3 Robiquet et Boutron Charlard : Ann. Chim. et Phys., vol. xliv, 1830, pp. 353-82. 
