424 EXCRETION. 



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 proportion of phosphates in 

 the blood of the dog was greatly diminished by feeding with potato. Deprivation of food 

 diminishes the quantity of phosphates in the urine, but a certain proportion is discharged, 

 which is derived exclusively from the tissues. We have already noted the fact that the 

 products of disassimilation of the nitrogenized principles are never discharged in health 

 without being accompanied with certain inorganic salts, such as the chlorides, sulphates, 

 and phosphates. 



In connection with the fact that phosphorus exists (in precisely what condition it is 

 not known) in the nervous matter, it has been stated that mental exertion is always 

 attended with an increase in the elimination of phosphates ; and this has been advanced to 

 support the view that these salts are specially derived from disassimilation of the brain- 

 substance. Experiments show that it is not alone the phosphates that are increased in 

 quantity under these conditions, but urea, the chlorides, sulphates, and inorganic matters 

 generally ; and, in point of fact, any physiological conditions which increase the pro- 

 portion of nitrogenized excrementitious principles increase as well the elimination of 

 inorganic matters. It cannot be assumed, therefore, that the discharge of phosphates is 

 specially connected with the activity of the brain. "We learn nothing from pathology 

 upon this point, for, although numerous observations have been made upon the excretion 

 of phosphoric acid in disease Vogel having made about one thousand different analyses 

 in various affections no definite results have been obtained. From these facts it is seen 

 that there is no physiological reason why we should connect the elimination of the phos- 

 phates with the disassimilation of any particular tissue or organ, especially as these salts 

 in some form are universally distributed in the organism. 



Observations have been made upon the hourly variations in the discharge of phos- 

 phoric acid at different periods of the day ; but these do not appear to bear any absolute 

 relation to known physiological conditions, not even to the process of digestion. 



Of the different phosphatic salts of the urine, the most important are those in which 

 the acid is combined with soda. These exist in the form of the neutral and acid phos- 

 phates. The acid salt has one equivalent of the base and is supposed to be the source of 

 the acidity of the urine at the moment of its emission. The so-called neutral salt is 

 slightly alkaline and has two equivalents of the base. The proportion of the phosphates 

 of soda in the urine is larger than that of any of the other phosphatic salts, but the daily 

 amount excreted has not been estimated. The phosphate of magnesia is a constant con- 

 stituent of the urine, as well as the acid and the basic phosphate of lime. The daily 

 excretion of phosphate of magnesia amounts to from 7*7 to 11'8 grains, and that of the phos- 

 phates of lime, from 4'7 to 5*7 grains. According to Robin, there always exists in the 

 urine a small quantity of the ammonio-magnesian phosphate, but it never, in health, 

 exists in sufficient quantity to form a crystalline deposit. The daily excretion of the phos- 

 phates is, as we have seen, subject to great variations, but the average quantity of phos- 

 phoric acid excreted daily may be estimated at about fifty grains, or, more accurately, 

 fifty-six grains. 



The urine contains, in addition to the inorganic principles above described, a small 

 quantity of silicic acid ; but, as far as we know, this has no physiological importance. 



Coloring Matter and Mucus. 



The peculiar color of the urine is due to the presence of a nitrogenized principle, 

 known to physiological chemists under a variety of names. We have mentioned it in the 

 table as urrosacine. It is also called urochrome, uroha9matine, uroxanthine, and purpu- 

 rine. We have no accurate account of its ultimate composition, and all that is known 

 about its constituents is that it contains carbon, oxygen, hydrogen, and nitrogen, and 

 probably iron. Although its exact ultimate composition is not absolutely settled, its con- 

 stituents are supposed to be nearly the same as those of the coloring matter of the blood, 



