146 GLUCOSIDES AND [CH. 



Prulaurasin (laurocerasin) is a glucoside occurring in the leaves of 

 the Cherry Laurel (Primus Laurowasus). It has been represented as 

 racemic mandelonitrile glucoside, prunasin being the dextro form. 



Sambunigrin is a glucoside occurring in the leaves of the Elder 

 (Sambucas nigra). It has been represented as laevo mandelonitrile 

 glucoside. 



When tissues containing cyanophoric glucosides and their corre- 

 sponding enzymes are submitted to autolysis, injury, or the action of 

 chloroform, hydrolysis takes place (see autolysis, p. 19). A rapid 

 method (Mirande, 17; Armstrong, 5) for detecting the prussic acid is to 

 insert paper dipped in a solution of sodium picrate into a tube con- 

 taining the plant material together with a few drops of chloroform. In 

 the presence of prussic acid the paper becomes first orange and finally 

 brick-red owing to the formation of picramic acid. 



In addition to those previously mentioned there are other British 

 plants, the leaves of which give off prussic acid on autolysis (presumably 

 from cyanophoric glucosides), as for example the Columbine (Aquilegia 

 vulgaris), Arum (Aram maculatum), Hawthorn (Crataegus Oxyacantha), 

 Keed Poa (Glyceria aquatica), Bird's-foot Trefoil (Lotus corniculatus), 

 Alder Buckthorn (Rhamnm Frangula), Black and Red Currant and 

 Gooseberry (Ribes nigrum, R. rubrum, R. Grossularia), Meadow Rue 

 (Thalictrum aquilegifolium) and the Common and Hairy Vetches ( Vicia 

 sativa and F. hirsuta). 



It has been shown (Armstrong, 7) that of the species L. corniculatus 

 there is a variety (L. uliginosus) (taller and growing in moister 

 situations) which does not produce cyanophoric substances and hence 

 does not give off prussic acid on autolysis. 



Expt. 140. Method of detection of cyanophoric glucosides in the plant. Take three 

 flasks: in one put a whole leaf of the Cherry Laurel (Prunus Laurocerasus] : in the 

 second a leaf which has been torn in pieces and then either pricked with a needle or 

 pounded in a mortar : in the third a leaf with a few drops of chloroform. Cork all 

 three flasks, inserting with the corks a strip of sodium picrate paper. (The paper is 

 prepared in the following way : strips of filter-paper are dipped in a 1 / solution of 

 picric acid, are then suspended on a glass rod and allowed to dry in air. Before 

 using, the paper is moistened with 10% sodium carbonate solution and is suspended 

 in the moist condition just above the material to be examined. In the presence of 

 prussic acid, the paper first becomes orange-yellow, then orange and finally brick-red.) 

 In a short time the paper in the flask containing the leaf and chloroform will turn red : 

 in the flask with the injured leaf, the reddening will take place rather more slowly, 

 whereas in the case of the entire leaf, the paper will remain yellow. 



The above experiment may also be carried out, usually with success, on leaves of 



