708 



PHYSIOLOGY 



animal a pure protein diet, we administer a mixed diet containing a 

 sufficient quantity of fat or carbohydrate, or of both substances, to 

 meet the normal energy requirements of the body, we can restrict 

 the utilisation of protein more nearly to the replacement of tissue 

 waste in the body, and are therefore able to attain nitrogenous 

 equilibrium with a much smaller proportion of protein than is possible 

 when this substance furnishes the whole diet. In carnivora, which 

 have the habit of supplying a large proportion of their energy needs 

 at the expense of protein, the amount of carbohydrate and fat which 

 must be added to protein in order to attain nitrogenous equilibrium 

 with a nitrogenous output equal to that in starvation is very large 

 and corresponds to an energy-value in excess of the total energy 

 expenditure during starvation. In omnivora, such as man, it is 

 easy to attain nitrogenous equilibrium on a mixed diet with a smaller 

 nitrogen turnover than is found during starvation. In the experi- 

 ment given on p. 701 the average nitrogen output during starvation 

 was about 12 grm. of nitrogen. In Succi, the fasting man, the nitro- 

 gen output varied from 11-19 grm. on the fifth day to 2-82 grm. on 

 the twenty- first day. 



DAILY NITROGEN EXCRETION OF STJCCI IN STARVATION 



Day 

 1 



2 

 3 

 4 

 5 

 6 

 7 



N. 

 5-05 

 4-32 

 5-4 

 3-6 

 5-7 

 3-3 

 2-82 



Chittenden has shown that in man a perfectly normal nutrition 

 may be maintained on a mixed diet containing about 7 grm. of nitro- 

 gen daily. In the cases investigated by Chittenden the energy 

 output of the men could be regarded as normal, corresponding to 

 32-35 calories per kilo body weight. If the amount of fat and 

 carbohydrate be very largely increased it is possible to maintain 

 nitrogenous equilibrium on even smaller quantities of protein. Thus 

 nitrogenous equilibrium was attained by Siven on a diet containing 

 33 grm. of protein daily (= 4 grm. of nitrogen), but in this case the 

 carbohydrates and fats were increased to such an extent that the man 

 was taking in 78-5 calories per kilo per day. These results suggest 

 that the qualitative metabolism of the body is determined by the 

 relative amount of food-stuff supplied to the body and circulating 

 in its juices at any given time, and that preponderance of one food- 

 stuff will tend to excite the cells of the body to the utilisation of this 

 food-stuff at the expense of the other two. That such is the case is 



