126 MANUAL OF CATTLE-FEEBING* 



standing by organized j[}rotehn tlie great mass of slowly 

 decomposing nitrogenous compomids in tlie body, and by 

 circulatory protein tlie relatively small quantity of easily 

 decomposable albuminoids which it contains. 



The quantity of circulatory protein in a poorly nourished 

 body is only small, not amounting in hmiger to one per 

 cent, of the weight of the organized albuminoids, but its 

 amount is increased by an abundance of protein in the 

 food, and may, at least in the carnivora, rise to five per 

 cent, or more. Eut, be the quantity of circulatoiy protein 

 large or small, the greater part of it, generally seventy to 

 eighty per cent., is consumed in the course of twenty-four 

 hours, and an exactly corresponding quantity of nitrogen 

 excreted in the urine as urea, etc. ; while of the organized 

 pi'otein, at most not more than 0.8 per cent, is consumed — 

 that is, the protein consumption in the body takes place 

 almost wholly at the expense of the circulatory protein. 



It can be by no means assumed, as was formerly done, 

 that all organs of the body are subject to a rapid metamor- 

 phosis, and that in the course of a comparatively short time 

 the whole organism to the last atom is renewed and rebuilt.' 



This is only the ease as regards a few tissues. The 

 blood corpuscles, e. ^., and the milk glands in the period 

 of their greatest activity, are rapidly destroyed and as 

 rapidly re-formed; but by far the greater part of the 

 organs have, w^hen once formed, a much greater stability, 

 although the contents of the cells vary much in quantity 

 and quality with the varying food o£ the animal. The 

 circulatory protein, on the contrary, suffers a continual and 

 rapid destruction, and must be contiimally replaced by 

 protein from the food. 



Other Experiments. — That the organized protein of 

 the animal body is destroyed far less easily than the circu- 



