652 COMPOSITION OF URINE. [BOOK n. 



normal pigment or pigments of urine is at present obscure and 

 the subject of much controversy. The matter 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 pigment which has been isolated and determined, 

 which has 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 normal 

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

 to a somewhat similar but different body, which in consequence 

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

 at the present moment, to make definite and satisfactory state- 

 ments 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 haematin 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 peculiar red colouring matter 

 occurring sometimes in the urine of acute rheumatism, which 

 has been called uroerythrin ; but our knowledge concerning these 

 is very imperfect. 



405. Ferments and other bodies. Even normal urine has 

 frequently been found to contain a small quantity, hardly amount- 

 ing to more than a trace, of proteid material, apparently an 

 albumin ; but the normal presence of even this small quantity has 

 been disputed. Urine, however, certainly contains ferment bodies. 



When urine is treated with many times its volume of alcohol, 

 a granular or flocculent precipitate is thrown down, consisting 

 chiefly of phosphates, together with some other substance or 

 probably several other substances, in very small quantities. An 

 aqueous solution of the precipitate, which may be freed from 

 the phosphates, is both amylolytic and proteolytic. Ferments 

 may also and more readily be extracted from urine by allowing 

 shreds of fibrin to soak in the urine for a few hours, and then 

 removing and washing them. The ferments become entangled 

 in the fibrin in such a way as not to be easily removed by 

 washing. The washed shreds will convert starch into sugar ; and 

 when treated with dilute hydrochloric acid digest themselves, 

 shewing the presence of pepsin. By this method it has been 

 ascertained that an amylolytic ferment and pepsin are present 

 in quantities which vary in the twenty- four hours according to 

 the meals. Rennin has also been found, and at times at least, 



