I.— PHYSIOLOGY. IGl 



analytic. There is more artistry about them. They are examples of the 

 creative instinct by means of which man from the earliest days has striven 

 to conquer Nature. But there is another reason for my choice of the 

 subject. A little more than a hundred years ago the first synthesis of a 

 product of animal life from inorganic matter — the production of urea from 

 ammonium cyanate — was described by Wohler. It seemed to me, there- 

 fore, an appropriate time to consider the bearing of the achievements of 

 organic chemical synthesis on our understanding of synthetic processes in 

 the living animal. 



Wohler's discovery did not bear immediate fruit. It required the 

 genius of Kekule with his hypothesis of the tetravalency of carbon and the 

 mode of linking of carbon atoms to point the way to a rational method 

 of illustrating the structure of carbon compounds, an organ of thought as 

 valuable as language itself. 



Once the structure of compounds could be pictured objectively it 

 became possible to build them up from others of known structure. How 

 aptly this exemplifies the dependence of progress on man's ability to 

 illustrate his conceptions pictorially ! Kekule's hypothesis came thirty 

 years after Wohler's synthesis, but from that time on we have seen and 

 acclaimed the discovery of the structure, in many instances confirmed by 

 synthesis, of a large number of organic substances which are produced by 

 living organisms. This discovery of the structure of products of cellular 

 activity is of prime importance to the physiologist. Structure is the point 

 from which we must always start when trying to find out how any particu- 

 lar substance is made in the cell. For this contribution to the solution of 

 our problems of synthesis, if for no other, we owe organic chemistry a great 

 debt. But the methods used by the chemist in synthetic processes have 

 usually been such as could have no place in the living cell with its extreme 

 sensitiveness to conditions such as temperature, reaction of the environ- 

 ment and osmotic pressure, to mention only the more obvious ones. The 

 use of high temperatures to bring about activation of the reacting sub- 

 stances is inadmissible. Activation in the living cell must be achieved 

 by other means. Acids and bases, except in such strength as will bring 

 about only small changes in hydrion concentration, cannot be employed. 

 All reactions must take place in an aqueous medium. With these and 

 other limitations it can readily be appreciated that a few only of the usual 

 processes of organic synthesis can be considered as operative in the cell. 



It is not possible within the scope of this address to consider all the 

 aspects of synthetic activity which are found in living organisms. Each 

 one presents almost a distinct problem. I propose, therefore, to deal only 

 with the animal cell, since its range of synthetic activity is narrower than 

 that of vegetable cells and has been more closely studied, and only with 

 the synthesis of a few substances which exemplify certain general problems. 



Unlike the Chemist, the animal cell has a very limited choice of raw 

 materials from which synthesis must start. These are the components of 

 the common foodstuffs. When they have undergone the preliminary pro- 

 cesses of digestion they provide in all about thirty substances which may 

 be regarded as available for the building up of new compounds by the cell. 

 They consist of about twenty amino-acids, two purine bases, three pyri- 

 midine bases, three hexoses, glycerol and higher fatty acids. It is true 



1930 M 



