PREFACE. 



This research was begun by me in October, 1902, and after considerable 

 preliminary laboratory investigation I found that in the solution of my 

 problems the crystallographic method promised at the present time to be 

 the most likely to yield satisfactory results. Not being an authority in the 

 science of crystallography, I associated with me in 1904 one of my colleagues, 

 Professor Amos Peaslee Brown, upon whom has fallen especially that por- 

 tion of the work which demanded the services of an expert crystallographer. 



The trend of modern biological science seems to be irresistibly toward 

 the explanation of all vital phenomena on a physico-chemical basis, and 

 this movement has already brought about the development of a physico- 

 chemical physiology, a physico-chemical pathology, and a physico-chemical 

 therapeutics. The striking parallelisms that have been shown to exist in the 

 properties and reactions of colloidal and crystalloidal matter in vitro and 

 in the living organism lead to the assumption that protoplasm may be 

 looked upon as consisting essentially of an extremely complex solution of 

 interacting and interdependent colloids and crystalloids, and therefore that 

 the phenomena of life are manifestations of colloidal and crystalloidal inter- 

 actions in a peculiarly organized solution. We imagine this solution to con- 

 sist mainly of proteins with various organic and inorganic substances. The 

 constant presence of protein, fat, carbohydrate, and inorganic salts, together 

 with the existence of protein-fat, protein-carbohydrate, and protein-inorganic 

 salt combinations, justifies the belief that not only such substances, but 

 also such combinations, are absolutely essential to the existence of life. 



The very important fact that the physical, nutritive, or toxic properties 

 of given substances may be greatly altered by a very slight change in the 

 arrangement of the atoms or groups of molecules may be assumed to be 

 conclusive evidence that a trifling modification in the chemical constitu- 

 tion of a vital substance may give rise to even a profound alteration in its 

 physiological properties. This, coupled with the fact that differences in cen- 

 tesimal composition have proved very inadequate to explain the differences 

 in the phenomena of living matter, implies that a much greater degree of 

 importance is to be attached to peculiarities of chemical constitution than 

 is universally recognized. 



The possibilities of an inconceivable number of constitutional differences 

 in any given protein are instanced in the fact that the serum albumin mole- 

 cule may, as has been estimated, have as many as 1,000 million stereoisomers. 

 If we assume that serum globulin, myoalbumin, and other of the highest 

 proteins may have a similar number, and that the simpler proteins and the 

 fats and carbohydrates, and perhaps other complex organic substances, may 

 each have only a fraction of this number, it can readily be conceived how, 

 primarily by differences in chemical constitution of vital substances, and 

 secondarily by differences in chemical composition, there might be brought 



