The Origin of Osmotic Effects. 



589 



other anesthetics in stimulating enzyraic activity in leaves ; in particular we 

 were impressed by the wonderful delicacy and elegance of the method 

 developed by Guignard of demonstrating the liberation of hydrogen cyanide 

 in the case of leaves containing cyanophoric glucosides by means of paper 

 coloured orange-yellow with an alkaline solution of sodium picrate — if 

 subjected to the action of hydrogen cyanide, such paper is at first coloured a 

 brown-orange, then rose-red and finally a dark brick-red. The test is one of 

 surprising delicacy. 



If a laurel leaf be enclosed in a test tube together with a slip of the 

 moistened paper, no alteration is observed in the colour of the paper even at 

 the end of several weeks ; if a minute drop of chloroform be introduced, the 

 colour changes within a very few minutes. 



Mirande, in the note rmder consideration, calls attention to the method 

 as being applicable to the detection of cyanophoric glucosides in plants 

 generally. 



Guignard, by whom Mirande's note was presented to the Academy, 

 discusses the subject from a wider point of view, with reference to observations 

 of a similar character which he has had occasion to make in recent years on the 

 decomposition of the glucoside in cruciferous plants. In particular, he calls 

 attention to the similarity in the effects produced by anaesthetics and by cold. 



The stimulative influence exercised by chloroform is specially striking in 

 view of the remarkable efficiency as inhibitants of vital activity of substances 

 so inert as chemical agents as toluene and naphthalene. Having long sought 

 for an explanation of such effects, we have welcomed the opportunity afforded 

 by Guignard's test of ascertaining what class of substances would condition 

 enzymic activity in the leaf. 



At the outset, in appeared probable that the leaf surfaces and cellular 

 membranes would act as differential sejjta and that the problem might 

 advantageously be treated from the point of view developed by Adrian J. Brown 

 in his recent striking and suggestive communication to the Society* on the 

 selective properties of the membrane surrounding the barley grain. Not only 

 has this proved to be the case but on account of the escape of hydrogen 

 cyanide whenever penetration takes place, of the ease with which the test 

 is applied and its extreme delicacy, leaves of plants containing cyanophoric 

 glucosides are, in not a few respects, superior to cereal grains as test objects ; 

 the latter are perhaps best used in determining the effect various solutes have 

 in regulating the extent to which an inflow of water takes place. 



* " The Selective Permeability of the Covering of the Seeds of Hordeum vulgare." 

 By Adriau J. Brown. 'Roy. Soc. Proc.,' B, 1909, vol. 81, p. 81 ; cf. "The Origin of 

 Osmotic Effects. II. — Differential Septa." By Henry E. Armstrong. Ibid., p. 94. 



