CHEMICAL DYNAMICS OF ANIMAL NUTRITION 125 



vary with the diet, and exogenous metabolism, which is responsible for 

 the greater part of the urea, and other varying constituents. According 

 to Folin then, the only nitrogenous matter necessary for the main- 

 tenance of equilibrium is that required to supply the waste represented 

 by the endogenous metabolism. Any superfluous nitrogen is eliminated 

 as rapidly as possible in the form of urea. 



We have, therefore, widely different views as to the function of 

 the nitrogenous constituents of the food-stuffs ; on the one hand we 

 have the view that the products of digestion are built up into the 

 tissues, and that, relatively, large amounts of albumen are necessary to 

 maintain the organism in full bodily vigour ; on the other hand we 

 have the view that only small quantities are necessary just the amount 

 that is required for the repair of the tissue waste which is continually 

 taking place, and that the main part of the bodily energy is derivable 

 from the non-nitrogenous constituents of foods. 



Which of these views, if either, is correct ? What is the true 

 function of nitrogen in the economy of nutrition ? With the object of 

 obtaining an answer to these questions, the following researches were 

 undertaken. 



METHODS OF RESEARCH 



Our ignorance is to be largely ascribed to the paucity of our 

 methods of research. Most of the older theories are based on 

 experiments which had for their object the determination of the balance 

 between ingesta and egesta, either by the analysis of inspired and 

 expired air (Zuntz, Speck, etc.), or by the estimation of nitrogen 

 in food and excreta (Pflilger, Voit, etc.), or by the estimation of 

 caloric values (Rubner, etc.), or by a combination of all these methods 

 of experiment (Atwatcr). 



The systematic determination of the distribution of nitrogen 

 amongst the various nitrogenous constituents of urine by the method 

 of Folin already referred to marks a distinct advance in the study of 

 metabolism. 



An attempt has been made in the following researches to throw 

 some light on the mechanism of nutrition by an entirely different 

 method. It was assumed that if the products of albumen degradation 



