626 NITROGENOUS METABOLISM. [BOOK n. 



presence of the food. This however is not the case as far as the 

 nitrogen of the meal is concerned; the larger portion passes off as 

 urea at once, and only a comparatively small quantity is retained. 

 If the diet be continued, and we are supposing the meals given to 

 be large ones, the proportion of the nitrogen which is given off 

 in the form of urea goes on increasing until at last 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 exclu- 

 sively 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 grins, 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. 



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 dis- 

 charged, 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 ( 385) 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 with 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 only about 7 p.c. was laid up as dry proteid material during 

 the fattening period, though the amount of proteid food was low. 

 This contrasts strongly with the amount of fat stored up during 

 the same period (see 400). Similar observations carried out 



