CHAP, v.] NUTRITION. 831 



a condition is established in which the nitrogen of the egesta 

 exactly equals that of the ingesta. This condition, which is spoken 

 of as " nitrogenous equilibrium," is attained in dogs with an ex- 

 clusively meat diet only when large quantities of food are given, and 

 is not easily maintained for any length of time. The exact quantity 

 of meat required to attain nitrogenous equilibrium varies with 

 the previous condition of the dog; equilibrium is frequently 

 attained when 1500 or 1800 grms. of meat are given daily. 



Thus the most striking effect of a purely nitrogenous diet is 

 largely to increase the nitrogenous metabolism of the body; and 

 we shall see later on that it increases the metabolism not only of 

 the nitrogenous but also of the other constituents of the body. 

 This great effect of proteid food in increasing the metabolism 

 of the body is shewn not only by the increase of urea but also by 

 the increase in the production of carbonic acid, and in the con- 

 sumption of oxygen. Thus when the respiratory interchange of 

 a man is watched and carefully measured from time to time, 

 a meat meal has been found to raise the production of carbonic 

 acid and the consumption of oxygen, until at the 3rd hour after- 

 wards the one reaches about 35 p.c. and the other about 32 p.c. 

 above what each was on a fasting stomach. And the effects of 

 heavy meat meals in the case of the dog have been found to be still 

 more striking and to last for a considerable time after the meal. 



The establishment of nitrogenous equilibrium does not mean 

 that a body-equilibrium is established, that the body-weight 

 neither increases nor diminishes. On the contrary, when the 

 meal necessary to balance the nitrogen is a large one, the body 

 though it is neither gaining nor losing nitrogen may gain in total 

 weight; and the increase is proved by calculation from the income 

 and output, and indeed by actual examination of the body, to be 

 due to the laying on of fat. The amount so stored up may be 

 far greater than can possibly be accounted for by any fat still 

 adhering to the meat given as food. We are therefore driven 

 to the conclusion that the proteid food is split into a urea moiety 

 and a fatty moiety, that the urea moiety is at once discharged, 

 and that such of the fatty moiety as is not made use of directly by 

 the body is stored up as adipose tissue. And this disruption of 

 the proteid, as we have already ( 487) suggested, explains at 

 the same time why the meat diet so largely and immediately 

 increases the urea of the egesta. 



This characteristic effect of proteid food to increase the 

 metabolism of the body is shewn on other animals besides the 

 dog, and not only by means of calculations of what is supposed to 

 take place in the body, but also by direct analysis. Thus the 

 analysis of the body of a pig, which had been fed on a known diet, 

 compared with the analysis of that of another pig of the same 

 litter, killed at the time when the first was put on the fixed diet, 

 gave as a result that of the dry nitrogenous material of the food 



