580 THE ANIMAL BODY AS A MACHINE 



that if this criterion were to be applied in Japan it would yield far 

 different estimates from those which would result from its application 

 in England. As Taylor has observed, the customary dietary of dif- 

 ferent races has in no small degree been fashioned by their ethnological 

 development. "In some lands races were compelled to adopt cultiva- 

 tion of the soil, in other places, fishing, in some areas the chase remained, 

 long into relative civilization, one of the chief methods of securing food. 

 The variations in ethnological development brought about by enforced 

 cultivation of the soil, as contrasted with the state of affairs in a tribe 

 of hunters, are well illustrated in different tribes of our American 

 Indians. Depending upon the method of sustaining the life of the 

 tribe, the standard diet of the tribe varied. Only under modern 

 conditions of transportation have the instincts and tastes of man had 

 opportunity for full choice in diet. Compulsion to some extent and in 

 some degree there has always been." 



Chittenden was able not only to maintain nitrogenous and calorific 

 equilibrium for prolonged periods on a much lower protein intake 

 than that recommended by Voit, but he was able to keep athletes in a 

 condition fitting them for extreme exertion. According to Taylor the 

 Nitrogenous Metabolism of a man of 70 kilos may be summarized as 

 follows, the nitrogenous output being expressed in terms of grams of 

 protein : 



Grams per 

 day. 



Nitrogen output on protein-free diet with carbohydrates . . . 10 to 15 



Nitrogen output in starvation, lowest level 15 to 20 



Nitrogenous and caloric equilibrium, with ample ingestion of carbo- 

 hydrate 30 



Nitrogenous and caloric equilibrium, largely with fat 40 



Normal protein input, safety margin of 100 per cent 70 



Nitrogenous and caloric equilibrium on a pure protein diet . . . 750 



Nitrogenous and calorific equilibrium can therefore be attained on a 

 diet rich in carbohydrates with a daily intake of only one-third of the 

 amount of protein recommended by Voit. It cannot be positively 

 affirmed that this low protein intake would also suffice to permit 

 normal growth in children or adolescents. It has been argued that as 

 a great part of even this small protein intake is simply deaminized 

 and burnt in the Exogenous Metabolism there must be plenty to spare 

 for tissue-synthesis. It has never been demonstrated, however, that 

 the exogenous metabolism is reducible below a certain level. In fact 

 the deaminization of amino-acids with production of urea continues 

 even in starvation. There is apparently, in so far as protein is con- 

 cerned, no level of the nutrient-reservoir at which a large overflow does 

 not occur. If the overflow and inflow are nearly balanced and the over- 

 flow (i. e., exogenous metabolism) is irreducible upon a diet of given 

 composition, then it is clear that the outflow of nutrients to the tissues 

 may be just sufficient to maintain repair and yet quite inadequate to 

 synthesize additional tissue, despite the fact that the intake is far above 



