4 INTRODUCTORY 



as vital products, although the glucoside itself may not have been 

 hitherto synthesised in all cases. 



The necessity for this treatment will be recognised when it is con- 

 sidered that the constituent atomic complexes of easily resolvable mole- 

 cules are very likely hereafter to be found in the free state in nature, 

 and in many instances are actually known, as in the case of glucose, 

 to exist as individual compounds. Thus, to mention another example, 

 hydroquinone (quinol) [7l] was at first entered as occurring only in 

 the form of the glucoside arbutin. "While this work was in course 

 of preparation it was announced by Hesse (Ann. 290, 3 17), that this 

 phenol occurs in the South African l sugar bush,' Protect, mellifera. 

 As the products from animals and plants are more and more investi- 

 gated it is certain that such instances will be multiplied. 



On considering the published records as to the occurrence of vital 

 products it also became evident that in very large numbers of cases 

 it was extremely doubtful in what form the compound was actually 

 produced by the animal or plant. In other words, it is uncertain 

 whether many compounds isolated, identified, and recorded as of 

 natural occurrence may not have resulted from the resolution of more 

 complex and unstable molecules by the action of enzymes or of the 

 chemical reagents employed in their extraction whether in fact they 

 may not have resulted from secondary changes or decompositions 

 taking place after removal from the organism. In view of this state 

 of affairs it must be admitted that a vital product is not so easily 

 definable as appears at first sight, and that in the present condition 

 of knowledge it is not always possible to say whether a particular 

 compound is of biochemical origin or whether it is a secondary 

 product. Under these circumstances it has been deemed advisable, 

 in order to make this work as comprehensive as possible, to assume 

 that the complex of atoms present in the molecule of the vital product 

 as isolated is of biochemical origin, even if the compound is not 

 directly synthesised as such by the animal or plant. 



This view will no doubt commend itself to both chemists and 

 physiologists. From the chemical standpoint it is certainly justifiable 

 to believe that if a complex molecule is so unstable as to break down 

 readily into simpler molecules, the atomic groupings present in the 

 latter pre-exist in their generator. Moreover, molecular instability is 

 a phenomenon of degree, and it has been found practically impossible 

 to define the conception narrowly in terms of the agents necessary for 

 causing the resolution of the compounds. It is not possible, for 

 example, to draw a hard and fast line between, on the one hand, the 

 action of enzymes and of acids or alkalies at ordinary temperatures, 

 and, on the other hand, the action of acids or alkalies at high tempera- 

 tures, or even, in the case of the more stable cyclic compounds, the 

 action of fused alkali. For this reason the conception of a vital 

 product has been enlarged so as to include every atomic complex 



