X] GLUCOSIDES 161 



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

 the Cherry Laurel (Prunus Laurocerasus). It has been represented as 

 racemic mandelonitrile glucoside, prunasin being the dextro form. 



Sambunigrin is a glucoside occurring in the leaves of the Elder 

 (Sambucus 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. 20). 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 containing 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 

 fi-om cyanophoric glucosides), as for example the Columbine (Aquilegia 

 vulgaris). Arum (Arum maculatum), Hawthorn {Crataegus Oxyacantha), 

 Reed Poa {Glyceria aquatica), Bird's-foot Trefoil (Lotus corniculatus). 

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

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

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

 sativa and V. 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. 



Ea^pt. 146. Method of detection of cyanophoric glvx;osides 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. 

 o. 11 



