PHYSIOLOGICAL 331 



There is a physics and a chemistry of the living body, and though 

 they do not when added up fulfil the role of biology, they are 

 indispensable aids to our understanding of the living creature. 



Our inquiry, then, is this. What big contributions has chemistry 

 made to biology, and what is it doing for biology to-day? It is plain 

 that most of the contributions must be to the physiological side of 

 biology; yet we shall see that chemistry is also helping embryology, 

 ecology or natural history, and even evolution theory. There is 

 necessarily some overlapping in this discussion ; yet it is worth while, 

 for our object here is what might be called methodological, to 

 illustrate from various sets of facts the indispensability of chemistry 

 to biology. 



There is no doubt as to where we should begin, for the initiator 

 of modem biochemistry was Lavoisier, at the time of the French 

 Revolution, that ill-fated genius whom the "Reds" of the Terror 

 guillotined, their very judge crying out in his madness that "the 

 Republic has no need of savants". Utilising the clue afforded by 

 Priestley's discovery (or re-discovery) of oxygen, Lavoisier first 

 made it clear that living implies combustion or oxidation of carbon 

 compounds, with the liberation of an oxide of carbon as a waste - 

 product. Lavoisier showed that life was literally a flame; he put the 

 living creature beside the lighted candle, and henceforth the burning 

 bush became the symbol of the living organism. 



Another of the fundamental contributions was made about half 

 a century later by the famous Liebig. For our present inquiry there 

 is great significance in the title of his well-known book (1840), 

 Chemistry in its Applications to Agriculture and Physiology, but we 

 wish mainly to associate his name with an idea that is fundamental 

 in physiology — the Circulation of Matter. Everyone is now familiar 

 with the flux of molecules from one linkage to another, the ceaseless 

 dance with changing partners, the passage of material from one 

 embodiment to another. Whether we think of the nitrogen cycle, 

 the carbon cycle, the sulphur cycle, the iron cycle, or any other, we 

 come in touch with biological problems of nutrition, development, 

 growth, and more besides. Animate Nature has evolved on a plan 

 that necessitates a cycle of reincarnations. All flesh is grass and all 

 fish is diatom ; and so the world goes round. Recent pioneering work 

 at the Rowett Institute at Aberdeen, on the importance of the 

 mineral constituents in the food of mammals and birds, illustrates 

 the far-reaching influence of Liebig's great idea. 



In some cases chemistry made contributions whose import was 

 hardly realised at the time, yet has continued increasingly. Thus, 

 about a generation after Lavoisier, a great step was made in 

 Wohler's sjoithesis of urea (1828). This was an epoch-making event, 

 for the building-up of this organic substance from simple inorganic 

 materials broke down at one blow the blockading wall between what 



