PHYSIOLOGICAL CHEMISTRY. 



INTRODUCTION. 



CHAPTER I. 



Scope and Methods. In our study of the organized world 

 the most fundamental problems which present themselves are 

 essentially chemical. Beginning with the mysterious trans- 

 formations wrought through the energy of the sun's rays in 

 such simple substances as the carbon dioxide and aqueous 

 vapor of the atmosphere, when these bodies come in contact 

 within certain vegetable cells, and following the history of the 

 products thus formed through their many changes in the 

 plant organism and later through the highly complex animal 

 structures, for whose formation the plant cell must prepare 

 the raw material, and finally as we note the gradual breaking 

 down of these same elaborate combinations, with liberation 

 of energy and ultimate restoration of carbon dioxide and 

 water and nitrogen to the air and soil which once had held 

 them, we see that, step by step, the various transformations 

 which occur are such as may be represented by the equations 

 of organic chemistry. It may not always be possible to 

 express these equations in simple or exact form, because of 

 the lack of knowledge in details, but the theoretical feasi- 

 bility of writing such expressions we everywhere recognize. 



In following the migrations of atoms of carbon, hydrogen, 

 oxygen and nitrogen through the vegetable and animal worlds, 

 our inquiry naturally widens beyond the field legitimately 

 claimed by chemistry. We find ourselves at the very outset 

 confronted by the question of the final forces inaugurating 



