THE MINIMUM OF PROTEIN. 



77 



reached sufficient to produce equilibrium between the income and outgo of 

 nitrogen. Two series of experiments were performed, in one of which the non- 

 nitrogenous nutrients consisted chiefly of fat, and another in which they con- 

 sisted of carbohydrates. Considering only those experiments in which the feed 

 consumed was more than sufficient in amount to supply the estimated demand 

 of the body for energy, it was found that when the nonnitrogenous nutrients 

 consisted of fat the nitrogen (protein) of the feed had to be increased to ap- 

 proximately 130 per cent of the amount katabolized in fasting before nitrogen 

 equilibrium was reached — that is, before the stock of body protein was main- 

 tained. When, however, the energy demands of the body were supplied by 

 carbohydrates instead of fats, a supply of nitrogen (protein) in the feed equal 

 to or even somewhat less than the amount katabolized in fasting sufficed to 

 insure nitrogen equilibrium. 1 Cremer and Henderson, 2 in experiments on a 

 dog with a ration estimated to supply the necessary energy for maintenance, 

 were unable to maintain nitrogen equilibrium on even as small an amount as 

 did Yoit and Korkunoff. 



In the case of man, on the other hand, numerous experiments seem to have 

 demonstrated that an amount of feed protein notably less than the ordinary 

 fasting katabolism is sufficient to maintain nitrogen equilibrium, although 

 even in this case the comparison in nearly every case is with the average 

 fasting katabolism and not with that of the individual under experiment. 

 This average for man, however, has been well established by numerous experi- 

 ments and seems not to vary widely for individuals, while in Benedict's ex- 

 periments 3 upon nutrition after fasting a material diminution of the protein 

 katabolism of the subject was observed on the second and third days. In every 

 case the body lost protein, but in experiments 70 and 74 there was a storing up 

 of energy. 



Protein katauolis?n during and after fasting.' 1 



Experi- 

 ments 69 

 and 70. 



Experi- 

 ments 71 

 and 72. 



Fasting: 



First day 



Second day . . 



Third day.... 



Fourth day . . 



Fifth day 



Sixth day 



Seventh day . , 

 Food after fasting: 



First day 



Second day . . 



Third day.... 



Grams. 

 60.5 

 85.6 

 90.2 



Grams. 

 35.0 

 66.2 

 78.6 

 64.4 



Experi- 

 ments 73 

 and 74. 



Grams. 

 61.7 

 71.8 

 69.2 

 62.3 

 59.9 



64. 44 

 49. 50 

 40. 68 



Experi- 

 ments 75 

 and 76. 



Grams. 

 73.4 

 74.7 

 78.1 

 69.8 

 65.2 

 64.4 

 60.8 



61.02 

 42. 90 

 46. 92 



Another factor which must be taken into consideration in fixing the minimum 

 of protein is what may be called the time element. Eubner calls attention 

 to the fact that if the protein of the ration is consumed at a single meal there 

 may be for a time a surplus of protein or its digestive products in the system, 



1 Yoit and Korkunoff put a different interpretation upon their results, basing it upon 

 the fact that a certain portion of the urinary nitrogen is derived from the nitrogenous 

 extractives of the flesh metabolized in the body. Compare the account of their experi- 

 ments in the writer's Principles of Animal Nutrition, pp. 135-139. 



2 Zeitschrift fur Biologie, vol. 42, p. 612. 



3 Loc. cit., pp. 456 and 529. 



4 The odd-numbered experiments were the fasting experiments. The even-numbered are 

 those in which food was given and which immediately followed the corresponding fasting 

 experiments. 



