SOURCES OF THE SALTS OF THE URINE. 263 



and an ammoniacal base being afforded by the like disintegra- 

 tion of albuminous compounds, whether of the food or of the 

 same solids. Chloride of sodium (common salt) holds a prin- 

 cipal place among the saline constituents of the urine, and 

 manifestly comes directly from the serum of the blood. The 

 phosphate of lime and the phosphate of magnesia are also 

 derived directly from the serum of the blood, yet it does not 

 follow, as is sometimes concluded, that they are derived im- 

 mediately from the food. These phosphates exist throughout 

 the solids, and in proportion as the solids undergo disintegra- 

 tion in a given time, these salts will in the mean time come by 

 absorption into the blood. Thus even when the weight of the 

 body is stationary, and when it is certain that the food contains 

 more earthy phosphates than the system requires, it is impos- 

 sible to pronounce that the earthy phosphates of the urine are 

 the identical earthy phosphates of the food ; all that can be 

 pronounced with certainty is, that as much of these phosphates, 

 from whatever source derived (wholly or in part), is thrown 

 off as has been, during a specified time, received in the food. 

 Neither is it true, as sometimes affirmed, that "the proportion 

 of these earthy phosphates in the urine appears entirely to de- 

 pend upon the amount ingested in the food ; " for if there has 

 been great muscular exertion prolonged for many hours, no 

 food being taken in the mean time, there is usually a large 

 proportion of these phosphates in the urine, plainly coming 

 solely from extensive disintegration of the living solids a fact 

 which has been long familiar to medical men. 



Of the alkaline phosphates and sulphates in the urine there 

 may be the same double source ; the one or the other source, 

 according to the circumstances of the case, being predominant. 

 Thus the phosphoric and sulphuric acid in these salts may be 

 formed by the oxygenation of phosphorus or sulphur contained 

 free either in the albuminous compounds used as food or in 



