. PRESIDENTIAL ADDRESS. 519 



In this disciiseion tvc shall have the advantage of the co-operation of Professor 

 Van Ronibiugli of Utrecht and Dr. GreshofVof Haarlem, wliose work with Dr. Treiib 

 of Java on this subjoct is known to chemists and botanists alike. The history of the 

 origin of the several investigations in which Dr. Henry has been associated with 

 me is not without interest in connection with the principal subject of this Address. 

 During the first British expedition to the Sudan against the Mahdi a number of 

 transport animals were poisoned through eating a small vetch which springs up 

 in the Nile Valley during the fall of the river. The plant {Lotus arabicus) is well 

 known to the Arabs, by whom it is cut when fully grown, and used as fodder for 

 animals. 



The results of the investigation of this matter which were communicated to 

 the Royal Society proved that the young plant generated prussic acid when 

 crushed with water. It was found to contain a new glucoside lotusin, together 

 with an enzyme capable of decomposing it into prussic acid, dextrose, and a 

 yellow colouring matter, lotoflavin. 



The glucoside is of special chemical interest, as being the only one known 

 which contains the cyanogen group attached in the molecule to the sugar residue. 

 Further investigation has shown that other fodder plants which are occasionally 

 poisonous owe this character to the existence of other cyanogenetic glucosides. 

 In a series of papers communicated to the Royal Society, Dr. Henry and I have 

 described the properties and constitution of dhurrin from Sorffhum vulgare, and of 

 phaseolunatin, which we have shown to be responsible for the production of prussic 

 acid by Fhaseolus lunatus (liima beans), Manihot iitilissima (cassava or tapioca), 

 and by linseed (the flax plant). Phaseolunatin is remarkable in furnishing acetone 

 as one of its products of hydrolysis. This investigation, besides fulfilling the 

 primary purpose for which it was carried out, has raised a host of problems ; — as to 

 the constitution of glucosides, the nature of the enzymes which accompany them in 

 the plants, and also in relation to the fundamental question of plant metabolism. 



Another subject of Imperial as well as National importance is to be the 

 subject of a joint discussion with the Section of Physiology. I refer to the 

 problem of diet. As chemists we are interested in this subject chiefly from the 

 point of view of the composition of foods, and of the molecular structure which is 

 associated with dietetic value. The first attempt to deal with the matter from the 

 scientific side was made by a great chemist, Liebig. We are now in a position to 

 investigate the problem more minutely, and the work of American physiologists 

 has already led to important results. We have still to learn how materials such 

 as rice and potatoes, which are nearly free from proteids, continue nevertheless 

 to serve as the main diet of large numbers of people. It would seem that the 

 best plan of operations will be for physiologists to settle by the accurate methods 

 now available the precise value of typical foodstuffs, and for the chemist to deal 

 with these in relation to their composition, and finally with reference to the 

 constitution of their constituents. The time has come when an advance must be 

 made from the chemical side in the analytical methods employed for gauging the 

 value of food materials. 



I feel that I have said much, but that I have left still more unsaid on many 

 topics. I must leave almost untouched the entire subject of mineral chemistry, 

 which is not only important in connection with the determination of the resources 

 of India and the Colonies, but is also a subject somewhat neglected on its 

 chemical side, which has been recently brought into prominence through the dis- 

 covery of radio-activity. 



The new radio-active mineral thorianite, from Ceylon, of which Mr. Blake and 

 I have given an account to the Royal Society, brings me at once to a subject which 

 raises the most fundamental of chemical questions, the nature of the elements and 

 of the atom. The recent discussions of this subject have become so purely specula- 

 tive that, whilst chemistry is bound to follow the lead of physics in this matter, 

 chemists are inclined to consider that more well-ascertained facts are needed for 

 any further discussion to be profitable from the purely chemical side. 



In this Address I have ventured to urge the fuller recognition by Government 

 of the scientific method as a powerful instrument in promoting the commercial 



