338 NUTRITION OF FARM ANIMALS 



herbivora. It seems a priori unlikely that such a difference in the 

 metabolic processes should exist, and later investigations have shown 

 that there is no such fundamental distinction between the various 

 species. It should be remembered, however, that the protein metab- 

 olism of herbivorous animals is often on a relatively low plane, and 

 that consequently relatively less ammonia may be available than in 

 the case of carnivorous animals. 



Another phase of the matter, which has received little considera- 

 tion, is the possibility that the long-continued presence of ammonium 

 salts in the body may have an injurious effect. The possibility of 

 injury through acid rations in this way could hardly be determined 

 except by means of experiments, covering; if possible, the whole life 

 cycle of the animal. 



Second, an excess of acid may be disposed of by combination 

 with the fixed bases present in the body. These are, in the 

 first instance, those contained in the carbonates and phosphates 

 of the blood and other fluids. Henderson, as already noted, 

 has shown that these salts are present in the blood serum in 

 such proportions that relatively large amounts of acids may be 

 disposed of in this way without materially altering the reaction 

 of the blood. 



c. Excretion of acids. The neutralization of acids produced 

 in the body does not, however, necessarily involve the excretion 

 of an equivalent amount of base. It is a familiar fact that the 

 urine may possess a considerable degree of acidity. The work 

 of Henderson shows that the kidneys are able to separate more 

 or less of the phosphoric acid from the bases of the blood, ex- 

 creting it as acid phosphates in the urine and retaining a cor- 

 responding amount of bases in the blood. 



428. The skeleton as a reserve of ash ingredients. The 

 store of bases in the body fluids, however, is limited. The larger 

 part of the ash of the body is contained in the skeleton, which 

 constitutes a relatively large reserve of basic phosphates and 

 carbonates which may be drawn upon to supplement the supply 

 in the blood. This fact has an important bearing on the ques- 

 tion of the necessary ash supply in the feed, while it must likewise 

 be taken into account in experimental work. Long-continued 

 maintenance on abnormal feeds or under conditions favoring 

 acid production in the body may result in extracting from the 

 body comparatively large amounts of mineral matter even to 



