CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 519 



invariably present in even healthy urine ; this however has not 

 as yet been placed beyond all doubt. Tin- nature of the .sub- 

 stances which give to urine its characteristic odour has not been 

 made out ; probably there are more such bodies than one. 



324. Pigments. Urine is always coloured, the tint vary- 

 ing from a light to a dark yellow with an admixture of bi . 

 In the course of twenty-four hours, a not incon.si.l.-raM.- quan- 

 tity of pigment must leave the body by the urine; but the 

 nature of the normal pigment or pigments of urine is at pres- 

 ent obscure and the subject of much controversy. The mat- 

 ter is apparently further complicated by the presence in urine 

 of what have been called ' chromogens,' that is to say, bodies 

 which are not coloured themselves but which readily give rise 

 to pigments upon oxidation ; and it is probable that some of 

 these ' chromogens ' of the urine are reduction products of the 

 respective pigments, the reduction taking place in the urine 

 after secretion, or during or even before secretion. There is 

 frequently present in urine, especially in cases of fever, a pig- 

 ment which has been isolated and determined, which lias a 

 characteristic spectrum, and which being maintained by some 

 to be a derivative of bilirubin, has been called urobilin. It is 

 not this urobilin however which gives to urine its ordinary 

 colour. Some observers, on the other hand, maintain that nor- 

 mal urine does contain and, in part at least, owes its normal 

 colour to a somewhat similar but different body, which in con- 

 sequence they have called ' normal ' urobilin. It is in fact not 

 possible, at the present moment, to make definite and satisfac- 

 tory statements as to whether urine contains one or more than 

 one normal pigment, as to its or their nature, as to whether 

 they are derived from bile-pigment or directly from the haemal in 

 of haemoglobin or in other ways, or as to the several steps by 

 which they are produced. There are also abnormal colouring 

 matters present on occasion, such for instance as the jHvuliar 

 red colouring matter occurring sometimes in the urine of acute 

 rheumatism, which has been called uroerythrin ; but our knowl- 

 edge concerning these is very imperfect. 



325. Ferments and other bodies. Even normal urine has 

 frequently been found to contain a small quantity, hardly 

 amounting to more than a trace, of proteid material, apparently 

 an albumin ; but the normal presence of even this small quan- 

 tity has been disputed. Urine, however, certainly contains 

 ferment bodies. 



When urine is treated with many times its volume of alco- 

 hol, a granular or flocculent precipitate is thrown down. Con- 

 sisting chiefly of phosphates, together with some other substance 

 or probably several other substances, in ver\ small quantities. 

 An aqueous solution of the precipitate, whirh may be freed fnnu 

 the phosphates, is both aiuylolytic and proteolytic. lYnnents 



