314 THE V&INE. 



better to resort to chemical tests. These have been described in 

 detail in the section on the Bile, and are directly applicable also to 

 the urine (see page 175). 



Other pigments also may occur in the urine after the ingestion of 

 various drugs, but as the products thus formed are of no special 

 interest from the standpoint of animal chemistry, they are not con- 

 sidered at this place. 



The Bile-acids. The occurrence of bile-acids in the urine is 

 solely a pathological phenomenon. In normal urines they are never 

 found, and even in complete obstruction of the common duct their 

 amount is quite small. To demonstrate their presence, they must 

 first be isolated as Platner's bile, and can then be identified by 

 polarimetric examination, their action upon the frog's heart, etc. 

 (see page 163). 



Fats, Cholesterin, and Lecithins. 



Fats. Traces of fat may be observed in the urine under normal 

 conditions when excessive amounts have been ingested. During 

 pregnancy also a lipuria has been noted, and is probably associated 

 with the development of the function of lactation. Otherwise the 

 condition is essentially a pathological phenomenon, and is notably 

 observed in acute yellow atrophy, in phosphorus poisoning, follow- 

 ing fracture of the long bones, etc. The largest amounts, however, 

 are found in cases of so-called chyluria. Owing to the existence of 

 the fats in fine emulsions, such urines may resemble milk in their 

 general appearance, and on standing a layer of "cream" forms at 

 the top. 



To establish the presence of fats, the surface layer of the urine is 

 extracted with ether, the ether is evaporated, and the residue brought 

 in contact with a piece of paper, when characteristic stains result. 



Gholesterin. Cholesterin is very rarely found in the urine, and 

 has thus far been encountered only under pathological conditions. 

 It probably always occurs in crystalline form, and is thus readily 

 recognized. If any doubt exists, the substance in question is 

 examined as has been described (page 180). 



Lecithins. Lecithins as such have been observed in the urine 

 only in chyluria, where they are commonly present in association 

 with cholesterin and fat. One of the derivatives of lecithin, how- 

 ever, is found also in the urine under normal conditions, though 

 in very small amounts. This is glycerin-phosphoric acid. It is no 

 doubt referable to decomposition of the lecithins of the food in the 

 intestinal canal, but may at times also be derived from the lecithins 

 of the tissues. To demonstrate its presence, several liters of urine 

 are freed from the common phosphates by rendering the urine 

 alkaline with barium hydrate and precipitating the heated mixture 



