v INTEENAL EESTITUTIVE SECRETIONS 329 



Unlike carbohydrate and fat, the protein of alimentary origin 

 cannot, outside very restricted limits, be stored up in the body in 

 a stable form. In fact, under normal conditions, and with a 

 regular diet, the adult organism excretes during the day (in the 

 form of urea and other nitrogenous waste products) approximately 

 the same amount of nitrogen as is introduced with the food, apart 

 from that which leaves with the faeces. The slight up and down 

 variations of the absorbed as compared with the excreted nitrogen, 

 the plus or minus that can be noted from day to day on a 

 sufficient diet, do not accumulate but tend towards compensation, 

 so that an almost perfect equilibrium of metabolism is obtained, 

 on comparing the sum total of the nitrogen introduced and 

 that given off in the space of a few days. Elsewhere we shall 

 discuss fully the modifications of the organic balance in regard to 

 the different individual conditions and the varying nature and 

 quantity of the food. 



Here we must confine ourselves to insisting on the fact that 

 while there is normally present in the tissues of the body a certain 

 provision of non-living protein, which constitutes a reserve of 

 nitrogenous material which can be utilised during a fast, and 

 readily replaced on the ordinary diet, this provision is invariably 

 confined within strict limits, so that it is not possible to increase 

 it (as can be done for fats, and to a certain extent for carbo- 

 hydrates) by an exuberant or luxus diet of nitrogenous substances. 

 Within physiological limits we constantly see that as the protein 

 introduced in the diet increases, so the amount of nitrogenous 

 waste products eliminated by the kidneys rises in proportion. 



This practically complete independence from the daily supply 

 of nitrogenous foods of the reserve protein stored up in the tissues, 

 shows clearly that only a minimal part of the total amount of 

 alimentary protein reaching the circulation is converted by the 

 anabolic activity of the cells into living matter, to repair the 

 perpetual losses suffered by the cytoplasm in its intimate structure 

 the greater part (which fluctuates enormously according to 

 the poverty or excess of the habitual diet) being consumed by 

 the katabolic activity of the tissues before it can become part of 

 the bioplasm. So that the nitrogen of the waste products daily 

 excreted comes to a large extent directly from the nitrogen of 

 alimentary protein. 



The process by which the consumption of alimentary protein 

 takes place within the tissues is quite unknown to us. We can 

 only state that it differs essentially from that by which protein 

 is broken up in the gastro- intestinal canal by the action of 

 the digestive enzymes. According to Neumeister (1890), living 

 tissues never convert protein into proteoses and peptone. We 

 have seen that the protein in the liver gives rise to the 

 nitrogenous and sulphur-containing constituents of the bile, which 



