ORGANS OF THE BODY. 531 



The following are the principal constituents of urine, as far as the pre- 

 sent state of science enables us to enumerate them with any certainty : 

 urea, kreatin, and kreatinin, xanthin, and hypoxanthin, uric, hippuric, 

 and oxalic acids, extractives, colouring matters, indican, and salts. Grape 

 sugar is probably also constantly present in the urine (Brucke)^ as well as 

 oxalic acid (combined with lime), phenol, and taurol (Stcedeler). The 

 whole amount of solid ingredients varies much in the course of the day, 

 ranging from 40 to 70 grammes. 



Urea ( 28) is found in the large proportion of from 2 '5 to 3 per cent, 

 in normal urine, or to the amount of from 25 to 40 grammes per diem. 

 This can, however, only be regarded as an approximate estimate. Its 

 quantity is not increased by muscular exertion ( Voit), contrary to an old 

 and widely-spread theory. But under a diet consisting largely of animal 

 food, it rises in amount ranging from 52 to 53 grammes, and after purely 

 vegetable food or complete abstinence, its quantity becomes considerably 

 diminished, and may only amount to about 15 grammes, or even less, per 

 diem (Lelimann}. Copious draughts of water and excretiqn of the latter 

 through the kidney also increases its amount. Urea is the most important 

 end product of the nitrogenous tissue elements, and consequently of the 

 albuminous substances introduced into the system with the food. It 

 appears in many cases to be derived from uric acid, a fact not only 

 supported by the nature of its chemical constitution, but also by the 

 observations of Wohler, Frerichs, and Zabelin, that the injection of uric 

 acid into the circulation increases the amount of urea excreted with the 

 urine. Kreatin, however, has also been regarded as one of its sources. 

 The introduction, also, of certain other bases into the body occasions 

 likewise, it is believed, a rise in the quantity of urea eliminated. These 

 are glycerin, guanin, and alloxantin. 



Uric acid ( 25) presents itself, on the other hand, in far scantier 

 amount than urea. In round numbers its proportion may be stated as 

 about O'l per cent., and its quantity for the whole day from 0*5 to 0'9 

 grammes, descending even so low as 0*2 grammes. Under similar con- 

 ditions to those alluded to in discussing urea, its amount rises and falls 

 analogously, though not, perhaps, to the same degree. It is contained in 

 large quantities in the urine of the lower order of mammals. It frequently 

 presents itself in very large quantities during fevers, accompanied by 

 great disturbance of the functions of respiration, a fact which lends 

 additional support to the theory already alluded to, that the formation of 

 uric acid is but a preliminary step to the formation of urea. As to where 

 it is generated, we know as little as of urea. The products of its physio- 

 logical decomposition are, besides urea, allantoin ( 29), oxalic, and car- 

 bonic acids. Streaker's discovery, also, that the decomposition of uric 

 acid gives rise to glycin, promises farther light on this subject. Uric acid 

 is supposed to exist in the urine in combination with soda, held in solu- 

 tion by acid phosphoric acid. The sparing solubility of its salts is the 

 cause of those sediments in the urine observed so frequently on the cooling 

 of the latter in a saturated condition. The rose coloured or brick dust 

 precipitates so formed consist of urate of sodium. 



The appearance, further, of one of the decomposition products of uri- 

 acid in the urine is of great interest ; this, oxalic acid occurs combined 

 with ammonia (Schunk, Neubauer). 



Hippuric acid ( 26) appears, under normal conditions, to occur in 

 but small quantities in human urine, and to have a double origin. In the 



