228 A Manual of Veterinary Physiology. 



Considerable discussion has occurred with reference to 

 this theory of A'oit's of circulating and tissue albumin, and 

 it is generally considered that the line drawn by this able 

 observer between the two does not hold good, and that he 

 is not warranted in stating that urea is derived from that 

 portion of the proteid which never becomes a part of the 

 living body, and which he terms ' circulating albumin.' That 

 under ordinary circumstances a portion of the nitrogen taken 

 in does form urea and allied substances, whilst another por- 

 tion is stored up in the tissues, is undoubted ; but it by no 

 means follows from this that the urea moiety is not derived 

 from living tissue — in fact, the total weight of evidence is 

 against Voit, for, as Burdon Sanderson expresses it, the 

 production of urea and other nitrogenous metabolites is 

 exclusively a function of living material. 



So long, therefore, as we are careful not to regard the 

 circulating albumin as so much dead substance, no harm 

 can arise from the use of the terms ' circulating ' and ' tissue 

 albumin,' as expressing the idea that part of the proteid is 

 retained in the body and part cast off from it. 



All true proteids are equally capable of becoming part of 

 the tissues when taken as food ; but when albuminoids, 

 such, for instance, as gelatin, are consumed, they produce 

 the same amount of urea as an assimilable proteid, but the 

 animal loses flesh, viz., none of the material is stored up 

 in the system. 



Non-nitrogenous Food.— When animals are fed on an 

 exclusively fat or starch diet they soon succumb. It is 

 impossible to maintain life on a nitrogen-free diet. In 

 experiments made with fat and starch sonic proteid must, 

 therefore always be given at the same time. 



The most remarkable effect of proteid and fat being given 

 together, is the sparing destruction of the proteid : much less 

 is used in the system when fats are given than without 

 them: this is spoken of as the proteid-sparing action of 

 fats. The amount of albumin required l>y the system is 

 also diminished by the presence of carbo-hydrates; this is 

 an important feature in the feeding of herbivora, in the 



