THE PROTEIN REQUIREMENTS OF MANKIND 115 



that he has done more work and led a more active life in every 

 way during the period of this experiment, and with greater 

 comfort and less fatigue than usual. 



Two points of very great interest are brought out in the 

 records of these observations : one was the very complete utiliza- 

 tion of the daily food the loss of nitrogen to the body per day 

 through the faeces amounted to only 0-79 gramme on a mixed 

 diet, containing a considerable quantity of matter not specially 

 concentrated ; the other is that this establishment of nitrogen 

 equilibrium on a low protein intake was accomplished without 

 increase in the daily intake of non-nitrogenous foods. During the 

 periods of six days, when the nitrogen balance was investigated, 

 the average heat value of the food per day was only a little over 

 1,600 calories. 



Taking the data recorded, with an average body weight of 

 57 kilos, and with an average daily elimination of nitrogen for 

 nearly nine months of 5-7 grammes, it is evident the nitrogen 

 metabolized per kilo of body weight was exactly 0-1 gramme. 



This is certainly a most remarkable result, even when the 

 facts that Chittenden's body weight is well below the average, 

 and that his activity was mental rather than physical, are taken 

 into account. Different partial explanations have been advanced 

 which would show that the experiment was carried out under 

 the most favourable conditions for a minimum intake of protein, 

 and for a low potential energy of the dietary. But no mental 

 suggestion nor simplicity in the routine of life will explain how 

 an average man carries on the ordinary duties of a professional 

 worker for a period of seven years, according to Chittenden's 

 latest statement, on a diet whose fuel value is only 1,600 calories, 

 or 28 calories per kilo of body weight, unless the average amount 

 hitherto considered absolutely necessary viz., about 40 calories 

 per kilo of body weight is far above the true requirements. There 

 are only two other possible explanations : either there is some 

 fallacy in the figures giving the data during the two periods of six 

 days each when a nitrogen balance was struck, so that they do 

 not accurately represent the conditions that obtained during the 

 whole period of observation, or, if the results obtained from 

 this experiment are to be extended to mankind in general, the 

 law of the conservation of energy as applied to human beings 

 must be seriously called in question. 



In this connection may be pointed out the surprisingly small 



