394 COMPOSITION OF URINE. [BOOK 11. 



The phosphates are derived partly from the phosphates taken 

 as such in food, partly from the phosphorus or phosphates peculiarly 

 associated with the proteids, and partly from the phosphorus of 

 certain complex fats such as lecithin. When urine becomes alkaline, 

 the calcic and magnesic phosphates are precipitated, the sodium 

 phosphates remaining in solution. The sulphates are derived 

 partly from the sulphates taken as such in food and partly from 

 the sulphur of the proteids. The carbonates, when occurring in 

 large quantity, generally have their origin in the oxidation of such 

 salts as citrates, tartrates, &c. The bases present depend largely 

 on the nature of the food taken. Thus with a vegetable diet, the 

 excess of the alkalis in the food reappears in the urine ; with an 

 animal diet, the earthy bases in a similar way come to the front. 



3. Nitrogenous crystalline bodies, derivatives of the metabo- 

 lism of the proteids of the body and food. First and foremost 

 come urea and its immediate ally, uric acid. These will be con- 

 sidered in detail hereafter; they are the typical products of the 

 metabolism of proteids. Existing in much smaller quantities are a 

 number of bodies more or less closely related to urea, which may for 

 the most part be regarded as less-completely oxidised products of 

 metabolism. Such are : kreatinin, xanthin, hypoxanthin, and 

 occasionally allantoin. To these may be added hippuric acid, 

 ammonium oxalurate, and, at times, taurin, cystin, leucin, and 

 tyrosin. These too we shall have to consider in dealing with the 

 metabolism of the body. 



4. Non-nitrogenous bodies. These exist in very small quan- 

 tities, and many of them are probably of uncertain occurrence. 

 They are organic acids, such as lactic, succinic, formic, oxalic, phe- 

 nylic, &c. It has been maintained that minute quantities of sugar 

 are invariably present in even healthy urine ; this however has not 

 as yet been placed beyond all doubt. 



5. Pigments. These are at present very imperfectly under- 

 stood. Whether the natural yellow colour of urine be due to a 

 single pigment, or to more than one, and what is the exact nature 

 of these pigments, must be left undecided. As was stated above 

 (p. 300), the urine frequently contains urobilin ; and the peculiar 

 red colour of some rheumatic urines is due to the presence of a 

 body called purpurin or uroerythrin. The urine of many animals, 

 especially of the dog, and occasionally of man, contains indican, 

 which under certain circumstances may give rise to the production 

 of indigo-blue. 



6. Other bodies. When urine is treated with many times its 

 volume of alcohol, a granular or flocculent precipitate is thrown 

 down, consisting of phosphates, some substance or substances giving 

 proteid reactions and probably other bodies in small quantities. 

 An aqueous solution of the precipitate is both amylolytic and 



