METABOLISM 3 



itself into the question, How much protein is required 

 to make good the daily destruction of tissue? This 

 question is one of such enormous practical importance 

 to the physician that a little space must be devoted to a 

 statement of the prevailing physiological views upon it. 



How much Protein is required? If one attempts 

 to solve this problem by the simple method of estimating 

 the amount of nitrogen excreted daily, one is at once 

 met by the difficulty that ' nitrogenous equilibrium ' can 

 be maintained on very varying quantities of protein. 

 The more protein the food contains, the more nitrogen 

 is excreted, and this goes on until the limits of the 

 digestive capacity are reached. If, again, one takes 

 the amount of nitrogen excreted during fasting as the 

 basis for constructing the diet sheet, it is found that if 

 this amount alone be supplied it is insufficient to 

 maintain equilibrium, and nitrogen is lost from the 

 body. At what point above this, . then, is one to fix 

 the proper quantity? Despairing of any experimental 

 solution of this problem, the older school of physiologists 

 fell back on purely empirical observation. They esti- 

 mated the amount of protein actually consumed by 

 groups of individuals on freely chosen dietaries, and 

 took this as the answer to the question. It was in this 

 way that Voit arrived at the standard of 118 grammes, 

 which was long accepted as the proper amount of 

 protein for the diet to contain, and it was upon this 

 estimate that the prevailing 'standard dietaries' were 

 constructed. Within the last few years, however, 

 physiologists have begun to question the correctness of 



the Voit standard. Investigation of the diets of many 



12 



