130 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



come in part from without, and are in part formed within the organism 

 through oxidation processes occurring within the body. Thus, after the 

 ingestioh of various vegetable matters containing vegetable acids the 

 urine of omnivorous animals becomes alkaline through the elimination 

 of carbonates of the alkalies, thus explaining the alkaline reaction of 

 the urine of these animals. Carbonates of the alkalies so formed in the 

 animal body, or when taken in foods, may be eliminated in this manner 

 through the urine, or they may themselves undergo decomposition, and 

 their carbon dioxide be eliminated through the lungs. When present in 

 solution they seem to assist in the various processes of oxidation 

 occurring in the body; they appear to assist in the emulsification of fats, 

 and in the blood the neutral carbonates of the alkalies appear to serve 

 in part as carriers of the carbon dioxide of the blood. They further 

 may modify the physical processes of diffusion occurring within the 

 mism. 



5. CALCIUM CARBONATE (C0 3 Ca). Calcium carbonate is a normal 

 constituent of the shell of birds' eggs, of the bones and teeth, the urine 

 of herbivorous animals, the parotid saliva of the horse, and is the prin- 

 cipal constituent of the so-called otoliths, or the small, inorganic masses 

 found in the internal auditoiy organs of man and different animals. In 

 the animal body it is partly in a state of solution and partly deposited 

 in the solid form. In the former condition it is found in the urine and 

 saliva of the herbivora, where its solution is rendered possible by carbon 

 dioxide. In the solid form it is deposited either in amorphous or 'crys- 

 talline form, as in deposits of sediment in the parotid saliva of the dog 

 and in the urine of herbivora. It originates from without, either in the 

 water taken internally or as a carbonate in vegetable food. The latter 

 explains its abundance in the urine of the herbivora, where the calcium 

 salts of organic acids are decomposed into carbonates. Only a part of 

 the calcium carbonate which enters the organism from without leaves it 

 as such. In many cases, as in man, it undergoes decomposition into 

 calcium phosphate. Its importance for the animal economy is not thor- 

 oughly understood. 



6. MAGNESIUM CARBONATE (C0 3 Mg). This salt is frequently a com- 

 panion of calcium carbonate, particularly in the urine of herbivora. Its 

 presence in bony tissue is apparent!}' doubtful. It has been found in 

 human urinary calculi, but only in small amounts. The herbivorous ani- 

 mals in their food nearly alwa3 r s absorb considerable amounts of mag- 

 nesium phospate, and since this salt is absent from their urine it would 

 appear that the magnesium carbonate is formed in the animal body from 

 the magnesium phosphate of vegetable food. 



7. ALKALINE PHOSPHATES (PO 4 Na 8 , P0 4 ^a 3 H, P0 4 NaH 2 , P0 4 K 8 , 

 P0 4 K a II, P0 4 KH a ). Phosphates of sodium and potassium are constant 



