PRINCIPLES OF BIOCHEMISTRY. 



INTRODUCTION. 



THE NATURE AND SCOPE OF THE SUBJECT. 



The subject-matter of biochemistry is the application of the known 

 principles of chemistry and physical chemistry to the study and inter- 

 pretation of life-phenomena; of the processes, that is of digestion, 

 assimilation, respiration, growth, reproduction, muscular contraction 

 and the like, which combine to distinguish living from inanimate 

 matter. From this definition it must be clear that biochemistry 

 possesses very close affiliations with both animal and vegetable physi- 

 ology. For physiology is the study of the way in which societies, indi- 

 viduals, organs and cells perform their functions, and since each and 

 every function of living matter ultimately involves or depends upon 

 chemical changes, to this extent the study of each and every function 

 of living matter becomes a part of the subject-matter of biochemistry. 



The distinction between physiology and biochemistry is in fact an 

 arbitrary one, depending very largely upon convenience and upon the 

 contemporary limitations of our knowledge. 



So long as we possess no clue whatever to the nature of the processes 

 which underlie or accompany a life-phenomenon, the study of that 

 phenomenon and of the method of its performance is, beyond any 

 question, an exclusively physiological problem. But directly we take 

 the first steps toward ascertaining the nature of the chemical phe- 

 nomena which accompany its performance, we are taking, also, the 

 first steps toward incorporating this problem into the subject of 

 biochemistry. 



The historical growth and development of the subject have illustrated 

 very aptly these natural applications. In the beginning, and that only 

 one brief generation ago, biochemistry was an undifferentiated portion, 

 a minor branch of physiology, and formed the subject of a bare half- 

 dozen lectures delivered by the professor of physiology. Gradually 

 the need of special training for the study of this subject, and its con- 

 tinually increasing magnitude and practical importance have led men 

 to make a special study of it, apart from that of the parent-subject. 

 The labors of these men have quickly added countless phenomena 

 to their special domain, and so important are these, and so funda- 

 mental is the part which biochemistry now plays in medicine, agri- 

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