CONSTITUTION OF THE URINE. 775 



tinal canal. More fluid is excreted by the kidneys in winter than in 

 summer, the skin being less active in the former, and more so in the 

 latter season. The quantity is said to be increased under higher bar- 

 ometric pressure. The specific gravity of the urine differs much, not 

 merely according to the different proportions, but also according to 

 the different nature of its solid constituents ; in health, it may range 

 from 1015 to 1030; usually, however, it deviates only slightly from 

 1020. The urine excreted after drinking much water, and taking 

 little or no food, which is named urina potus, is of course of low spe- 

 cific gravity ; that after eating a full meal, is of high specific gravity, 

 and is called urina cibi vel chyli ; whilst after complete abstinence 

 from both food and drink, as in the morning, it is most completely 

 saturated with solid constituents, and is therefore at its highest spe- 

 cific gravity ; it is then called urina sanguinis. The amount of solid 

 constituents is irrespective of that of the fluid, and depends on the 

 activity of the metamorphosis of the tissues, and of the superabundant 

 food. Its usual bright amber color varies, according to its density, 

 from that of a colorless fluid to a deep yellowish-brown. In disease, 

 the color and specific gravity present important variations ; thus, in 

 Bright's disease of the kidneys, the specific gravity may be as low as 

 1003, being little higher than that of water ; its proper constituents 

 are then deficient, whilst albumen, derived from the plasma of the 

 blood, is present ; on the other hand, in diabetes mellitus, in which the 

 urine contains sugar, the specific gravity may be as high as 1050. 

 The .peculiar odor of the urine is strongly developed by a heat suffi- 

 cient to produce evaporation. The natural reaction of this fluid is 

 acid, but after digestion, and especially after a vegetable diet, it may 

 become alkaline; in herbivorous animals, this is its normal character. 

 The cause of its acidity will be discussed after its chemical composi- 

 tion has been described. From a particular kind of decomposition, 

 known as the acid fermentation, its acidity may be increased, after it 

 has been excreted ; on the other hand, by a decomposition of the urea, 

 in which carbonate of ammonia is generated, it may acquire a strong 

 alkaline reaction a few hours after its excretion, or even, in certain 

 diseases, whilst it is yet retained in the bladder. In such a condition, 

 an abnormal deposit of phosphates takes place. 



Normal urine consists of water, holding a very variable quantity 

 viz., from 2 to 7 per cent. of solid substances, of which urea is the 

 chief; besides this, there are uric and hippuric acids, free carbonic 

 acid, often lactic acid, occasionally oxalic acid, extractive nitrogenous 

 matters, partly crystallizable, such as creatin and creatinin, xanthin, 

 phenylic, carbolic, benzoic, and other acids, uncrystallizable extractives 

 of uncertain composition, small quantities of special pigments, traces 

 of fatty matter, numerous salts, such as sulphates, phosphates and 

 chlorides of potash, soda, lime, and magnesia, with silica, mucus, and 

 epithelium. The relative proportions of its various solid constituents 

 in 100 parts, and the daily average quantity of each, excreted from 

 every 1 lb. weight of the body, in a man weighing 145 Ibs. avoirdu- 

 pois, are shown in the annexed Tables. 



