THE PIGMENTS OF THE URINE. 307 



Esbach's reagent, which consists of an aqueous solution containing 

 10 grammes of picric acid and 20 grammes of citric acid to the 

 liter, is then added to the mark R. The tube is closed, inverted a 

 number of times, and set aside for twenty-four hours. The number 

 of the scale which corresponds to the height of the precipitated 

 albumins indicates the amount in grammes in 1000 c.c. of urine. 

 Care must be had, however, that the urine is acid, that the density 

 does not exceed 1.006-1.008, and that the temperature remains at 

 about 15 C. 



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 Kjeldahl's 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 on reduction. 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 the disappearance 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 oxidation to 

 choletelin. This view of the origin of urobilin, of course, does not 

 necessarily preclude the possibility that a certain amount of the pig- 

 ment, 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 re- 

 lated, we are scarcely in a position to speak authoritatively of the 



