METABOLISM, NUTRITION AND DIETETICS 533 



equivalent to this amount that is to say, about 34 grammes 

 of dry protein, or 175 grammes of lean meat the excretion of 

 nitrogen would at once have leaped up to nearly double its 

 starvation value. If the quantity of protein in the diet was 

 progressively increased, the output of urea would increase along 

 with it, but at an ever-slackening rate ; and at length a con- 

 dition would be reached in which the income of nitrogen exactly 

 balanced the expenditure, and the animal neither lost nor gained 

 flesh. 



In an experiment of Voit's, for instance, the calculated loss of 

 flesh in a dog with no food at all was 190 grammes a day. The 

 animal was now fed on a gradually increasing diet of lean meat, with 

 the following result. 



The loss of nitrogen in the urine and faeces is what was measured. 

 Knowing the average composition of ' body-flesh ' (muscles, glands, 

 etc.), it is possible to translate results stated in terms of nitrogen into 

 results stated in terms of ' flesh.' Muscle contains approximately 

 3*4 per cent, of nitrogen. Here, with a diet of 480 grammes of meat, 

 the dog was still losing a little flesh ; it would probably have required 

 from 500 to 600 grammes for equilibrium. The results are graphi- 

 cally represented in Fig. 186, p. 535. 



The quantity of protein food necessary for nitrogenous 

 equilibrium varies with the condition of the organism ; an 

 emaciated body requires less than a muscular and well-nourished 

 body. The least quantity which would suffice to maintain 

 in nitrogenous equilibrium the famous 35 kilo dog of Voit, 

 even in very meagre condition, was 480 grammes of lean meat, 

 corresponding to 16 grammes of nitrogen, or 35 grammes of 

 urea that is, about three times the daily loss during starva- 

 tion. From this lower limit up to 2,500 grammes of meat a 

 day nitrogenous equilibrium could always be attained, the 

 animal putting on some flesh at each increase of diet, until at 

 length the whole 2,500 grammes was regularly used up in the 

 twenty-four hours. A further increase was only checked by 

 digestive troubles. A man, or at least a civilized man, can con- 

 sume a much smaller amount both absolutely and in proportion 



