THE PROTEIN ELEMENT IN 

 NUTRITION 



CHAPTER I 



INTRODUCTION 



" The life-processes consist in the metabolism of the proteins." VERWORN. 



THE important part played by the complex body protein and its 

 allied nitrogenous compounds is acknowledged by all students of 

 nutrition. 



As a food material it is the one constituent that is indis- 

 pensable ; it is the only substance of the three main classes of 

 proximate principles that is absolutely essential for the carrying 

 out of those vital phenomena whose aggregate may be considered 

 to represent the processes of life. 



The more important tissues of both animal and vegetable life 

 consist largely of this protein material, and it is in connection 

 with the changes protein undergoes within the living organism 

 the chemical changes by which the protein of the food is prepared 

 for absorption and incorporation into the bioplasm, the changes 

 which it undergoes while it shares in the life of the tissues, and, 

 finally, those by which it is broken down again into waste 

 products and eliminated from the body it is in connection with 

 these that much of the interest in the subject centres. It is but 

 natural, therefore, that the chemistry of metabolic processes 

 should have attracted the attention of large numbers of investi- 

 gators. The result of this has been that the literature of the 

 subject has already attained enormous proportions. 



Progress, despite the vigorous activity displayed by a yearly 

 increasing number of workers in physiological chemistry, has 

 not been very conspicuous. In recent years, however, owing to 

 the introduction of new methods of attacking the problems 



