450 NITROGEXUUti METABOLISM. [BOOK n. 



deficient in flesh, it might be expected that the great mass of food 

 would be at once stored up, and only a small quantity be imme- 

 diately worked off as an additional quantity of urea, occasioned 

 by the increased labour thrown on the economy by the very 

 presence of the food. This however is not the case ; 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 sup- 

 posing the meals given to be ample 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 exclusively 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 equi- 

 librium varies with the previous condition of the dog ; it is fre- 

 quently seen 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. This result 

 has been explained by supposing that with the meat diet the 

 consumption of oxygen is largely increased ; in other words, that 

 the oxidizing activity of the body is directly augmented by a meat 

 diet. This in turn may be due in part to the fact that proteid 

 food largely increases the number of the red corpuscles, and so 

 augments the amount of oxygen with which the tissues are 

 supplied ; but as we have already urged more than once the 

 oxidative activity of the tissues is determined by the tissues 

 themselves rather than by the mere abundance of oxygen at their 

 disposal ; and probably other agencies are at work. 



When nitrogenous equilibrium is established, it 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 may 

 gain in weight, and the increase is proved, both by calculation 

 from the income and output, and 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 fat as is not made use of directly by the body is 

 stored up as adipose tissue. And this disruption of the proteid 

 food at the same time explains why the meat diet so largely and 

 immediately increases the urea of the egesta. We have already 

 pointed out that possibly this disruptive metabolism of proteids is 

 largely carried on in the alimentary canal itself by the aid of the 

 pancreatic juice ; whether or to what extent other organs share in 

 the action we do not at present know, 



