12 THE PROTEIN ELEMENT IN NUTRITION 



products of protein digestion, it did not matter to the body how 

 much protein the diet contained ; the result would be the same as 

 if no nitrogen were present in the food at all. The necessary 

 building-stones would have to be obtained from the disintegration 

 of the inferior tissues of the body in order that the master tissues 

 should be maintained as long as possible in a state of nutrition 

 and repair. When those particular building-stones are known 

 and can be supplied in the food, it has been found possible to 

 reduce the protein element of the dietary to a minimum. The 

 danger of such a procedure in the general dieting of mankind is 

 made apparent when it is recognized that the particular amino- 

 acids required in any given state of body nutrition cannot possibly 

 be known, and this danger is enhanced by the fact that in the 

 ordinary food materials, particularly in those of vegetable origin, 

 the amino-acids are not present in the proportions (sometimes 

 not present at all) necessary for the building up of tissue protein. 

 It is clear, therefore, that in the selection of a sufficiency of 

 suitable units a great many end-products of protein digestion 

 that are not required will be rejected their nitrogen split off, 

 and got rid of as urea. In order that the body may receive a 

 sufficiency of the particular units it requires, a good supply of 

 protein in the food is essential, a supply very much greater than 

 what would be necessary if the suitable combinations were 

 offered in the diet. 



But while it is true that within a few hours of the ingestion of 

 a protein meal seemingly a large part of its nitrogen is eliminated 

 as urea, it does not necessarily follow that the nitrogen split off 

 is of no service in nutrition. In fact, it is well recognized how 

 very important a part ammonia does play in those pathological 

 conditions where there is an over-production of acids within the 

 body. 



In acidosis and acid intoxications it is of the greatest impor- 

 tance that the acids formed should be disposed of in some way 

 without involving any reduction in the alkalescence of the blood. 

 This can be effected by the ammonia derived from protein 

 metabolism, and which is on its way to be changed into urea. 

 Ammonia is, therefore, of considerable interest as one of the 

 chemical defences of the body against disease. By combining 

 with and neutralizing organic acids, sometimes formed in ex- 

 cessive amounts, it permits of their elimination in the urine 

 without depleting the blood of its important bases. However, 



