ALKALINE AND EARTHY PHOSPHATES. 463 



rated during combination with the sulphur, is one of the 

 subordinate means by which the animal temperature is 

 maintained. 



Besides the sulphur in these salts, some also appears to 

 be in the urine, uncombined with oxygen ; for after all the 

 sulphates have been removed from urine, sulphuric acid 

 may be formed by drying and burning it with nitre. Mr. 

 Ronalds believes that from three to five grains of sulphur 

 are thus daily excreted. The combination in which it 

 exists is uncertain : possibly it is in some compound 

 analogous to cystin or cystic oxide (p. 464.). 



The phosphoric acid in the urine is combined partly with 

 the alkalies, partly with the alkaline earths about four or 

 five times as much with the former as with the latter. In 

 blood, saliva, and other alkaline fluids of the body, phos- 

 phates exist in the form of alkaline, probably tribasic, 

 salts. In the urine they are acid salts, viz., the bi-phos- 

 phates of soda, ammonia, lime, and magnesia, the excess 

 of acid being, according to Liebig, due to the appropriation 

 of the alkali with which the phosphoric acid in the blood 

 is combined, by the several new acids which are formed or 

 discharged at the kidneys, namely, the uric, hippuric, and 

 sulphuric acids, all of which he supposes to be neutralized 

 with soda. 



The presence of the acid phosphates accounts, in great 

 measure, or according to Liebig, entirely, for the acidity 

 of the urine. The phosphates are taken largely in both 

 vegetable and animal food ; some thus taken, are excreted 

 at once ; others, after being transformed and incorporated 

 with the tissues. Phosphate of lime forms the principal 

 earthy constituent of bone, and from the decomposition of 

 the osseous tissue the urine derives a large quantity of this 

 salt. The decomposition of other tissues also, but espe- 

 cially of the brain and nerve-substance, furnishes large 

 supplies of phosphorus to the urine, which phosphorus is 

 supposed, like the sulphur, to be united with oxygen, and 



