214 EXCKETTON. 



The remarks which we have just made with regard to the 

 chlorides and the sulphates are applicable, to a certain ex- 

 tent, to the phosphates. These salts exist constantly in the 

 urine, and are derived in part from the food, and in part 

 from the tissues. Like other inorganic matters, they are 

 united with the nitrogenized elements of the organism, and 

 when these are changed into excrementitious principles, and 

 are separated from the blood by the kidneys, they pass with 

 them and are discharged from the organism. 



It becomes a question of importance, now, to consider 

 how far the phosphates are derived from the tissues, and 

 what proportion comes directly from the food. This point 

 is peculiarly interesting, from the fact that phosphorus has 

 been shown to exist in the nerve-tissue, and it has been in- 

 ferred that the excretion of phosphates represents, to some 

 extent, the physiological wear of the nervous system. 



All observers agree that the quantity of phosphates in 

 the urine is in direct relation to the proportion in the food, 

 and that an excess of phosphates taken into the stomach is 

 immediately thrown off by the kidneys. 1 It is a familiar 

 fact, indeed, that the phosphates are deficient and the car- 

 bonates predominate in the urine of the herbivora, while the 

 reverse obtains in the carnivora ; and that variations, in this 

 respect, in the urine may be produced by feeding animals 

 with different kinds of food. Yerdeil made some very inter- 

 esting comparative analyses of the blood for the alkaline 

 phosphates in the herbivora, the carnivora, and in man*. He 

 found the proportion very small in the ox, as compared with 

 the dog, and intermediate in the human subject. The pro- 

 portion of phosphates in the blood of the dog was greatly 

 diminished by feeding with potato. 2 Deprivation of food di- 

 minishes the quantity of phosphates in the urine, but a certain 



1 NEUBAUER AND VOGEL, op. tit., p. 411. 



HAMMOND, On the Excretion of Phosphoric Add by the Kidneys. Physio- 

 logical Memoirs, Philadelphia, 1863, p. 29, et seq. 



2 ROBIN ET VERDEIL, Chimie anatomique, Paris, 1853, tome ii., p. 330. 



