THE PROTEIN REQUIREMENTS OF MANKIND 107 



of the body for energy are fully met by an abundant supply 

 of carbohydrates and fats. This amount may be regarded as 

 the minimum quantity of protein essential for existence, and 

 must be carefully distinguished from the quantity necessary to 

 maintain the body in the highest degree of efficiency. 



By none of the methods discussed above can a definite answer 

 be given to the question, What are the protein requirements of 

 the body ? The fact that the body is ever striving to adapt 

 the protein decomposition to the intake, and that it can establish 

 itself in a condition of nitrogenous equilibrium on very varying 

 quantities of protein, is the great cause of the difficulties that 

 beset the path of those engaged in finding a conclusive reply to 

 the above question. This power of the organism of being able 

 to maintain itself in nitrogenous equilibrium on the most diverse 

 amounts of protein could only mean that sooner or later con- 

 troversy must arise as to what particular level of interchange 

 is best for the efficiency, economy, and welfare of the body. The 

 question, therefore, instead of being, What are the protein needs 

 of the body ? becomes, What level of protein metabolism is most 

 advantageous ? 



As has been demonstrated at considerable length, it is the 

 universal opinion of those most interested in furnishing a correct 

 answer viz., mankind in general that at least 100 grammes of 

 protein daily is necessary if the body is to be maintained in a 

 condition of health and efficient for the average degree of labour 

 it is called on to perform ; that the protein requirement is in- 

 fluenced by work, hard labour demanding sooner or later an 

 increase in the protein constituent of the diet. Accepting for 

 the moment the recognized view that the energy of muscular 

 work comes from the carbonaceous and not from the nitrogenous 

 constituents of the body, the fact remains that increased labour 

 creates a demand for protein food. This demand is all the more 

 noticeable the poorer the ordinary foodstuffs are in their protein 

 content. In an ordinary mixed dietary this desire for protein 

 is met by an increase in the total amount of food consumed ; 

 but in tropical dietaries, which are usually highly carbonaceous, 

 and not infrequently bulky, a highly nitrogenous food is taken 

 in addition, or replaces some of the more carbonaceous materials. 

 This point is well exemplified by the great consumption of animal 

 food amongst those who do really hard labour in India and 

 Japan. With the mixed dietaries of Europe and America the 



