THE PIGMENTS OF THE URINE. 291 



If more accurate results are desired, a known volume of urine, 

 feebly acidified with nitric acid if necessary, is heated, first on a 

 water-bath and then over a free flame, until coagulation is com- 

 plete. The precipitate is collected on a small filter, and washed 

 with water, alcohol, and ether. The contained nitrogen is now esti- 

 mated according to Kjeldahl's method, when the result multiplied 

 by 6.3 will indicate the corresponding amount of albumin. 



If it is desired to estimate the amount of the individual albumins 

 separately, they are first isolated, as has been described, and are then 

 subjected to KjeldahPs process. In this case, however, ammonium 

 sulphate cannot be used for purposes of salting. 



THE PIGMENTS OF THE URINE. 



Of the chemical nature of the pigments of normal urine little is 

 known that is definite. According to some observers, the yellow 

 color is due, in part at least, to the presence of so-called urochrome, 

 which in turn is regarded as identical with the normal urobilin of 

 MacMunn. Others, again, claim that there is no reason to suppose 

 that a difference exists between this normal urobilin and the urobilin 

 of Jaffe, which is mostly observed under pathological conditions, but 

 which may occur also in health. Jaffe' s urobilin, further, is held by 

 some to be identical with the hydrobilirubin which results from 

 bilirubin through the action of sodium amalgam. Of late, how- 

 ever, this view has been questioned, especially as bilirubin on oxida- 

 tion furnishes a substance, choletelin, which cannot be distinguished 

 from hydrobilirubin on the one hand, or urobilin on the other. A 

 similar pigment, or one which is identical with urobilin, has further 

 been obtained from hsematoporphyrin. That the urobilin which is 

 notably observed under pathological conditions can be formed within 

 the body in the absence of micro-organisms is now a well-established 

 fact. We thus find that in diseases in which the elimination of bile 

 through the usual channels is prevented, urobilin may occur in the 

 urine, nevertheless ; and it has further been noted that both at the 

 beginning and at jthe end of jaundice increased amounts are found. 

 Similar results have been obtained when from any cause an increased 

 destruction of blood-pigment occurs. We may thus imagine that in 

 such cases the urobilin results from bilirubin through an extensive 

 oxidation to choletelin. This view of the origin of urobilin, of 

 course, does not necessarily preclude the possibility that a certain 

 amount of the pigment, which, as I have said, may normally also 

 occur in the urine, may be derived from bilirubin through a process 

 of reduction in the intestinal tract. But, as is apparent from the 

 considerations just related, we are scarcely in a position to speak 

 authoritatively of the origin of the normal urinary pigments. The 

 chemical position of the colorless mother-substance of urobilin, more- 

 over, which is spoken of as urobilinogen, and which can usually be 

 demonstrated whenever urobilin also is present, is thus far not clear. 



