BILE PIGMENTS AND THEIR DERIVATIVES. 383 



reddish-brown and grass-green. To the variation in relative amount of 

 these two pigments is also due the difference in colour between fresh 

 and stale bile. When bile stands in the gall bladder, its pigments 

 become reduced, the biliverdin is converted into bilirubin, and the 

 colour becomes yellow or brown. Fresh human bile has also a green 

 colour, but that observed in the post-mortem or dissecting-room is 

 always brown, because of this process of reduction. These two normally 

 occurring bile pigments are related to each other in a manner analogous 

 to haemoglobin and oxyhsemoglobin ; bilirubin (C 10 H 18 N 2 03) on oxidation 

 passes into biliverdin (C 16 H 18 N 2 4 ). 



Haycraft and Scofield 1 observed in the gall bladder itself reduction 

 going on, as shown by the fact that, while the bile in the middle of the 

 gall bladder was green, the thicker bile mixed with mucus near the 

 bladder wall was orange-brown, and the mucous membrane itself of a 

 brown colour. To this slow reduction Haycraft and Scofield ascribe 

 also the presence of bilirubin and not biliverdin in the gallstones of 

 oxen, although the latter is the chief pigment found in ox bile. Putre- 

 faction readily brings about the same reduction in the bile pigments. 

 Bile with the bilirubin tint predominant does not turn green from 

 oxidation of this pigment to biliverdin, when it is exposed to the air, 

 unless it be made strongly alkaline with caustic alkali. In this increased 

 readiness to take up oxygen in alkaline solution, bilirubin resembles a 

 large number of other organic substances, such as pyrogallol and pyro- 

 catechin. Haycraft and Scofield were also able to induce these changes 

 by the action of nascent oxygen and of ozone. Working with a battery of 

 four or five Grove cells, and leading from platinum electrodes into brown- 

 coloured bile (in a beaker or on filter paper), they found that the oxygen 

 developed at the anode caused in a few minutes a change in colour of 

 the bile, through green and blue into violet, followed by bleaching. On 

 reversing the poles, so that reduction instead of oxidation took place at 

 this spot, an inverse change in colour back to brown was observed. 



Bilirubin and biliverdin have chemically the character of weak acids, 

 as is shown by the ease with which they unite with bases to form salt- 

 like bodies. Such compounds with alkalies are soluble in water, but 

 with alkaline earths are insoluble; as, for example, the compound of 

 bilirubin with calcium, which makes up the bulk of red gall stones, and 

 forms a convenient source for the preparation of the pigment. Neither 

 pigment has a spectrum showing absorption bands, but in each there is 

 continuous absorption at the blue end of the spectrum. 



Bilirubin has borne in the history of the bile pigments many names, 

 such as cholepyrrhin,biliphain,cholephain, and bilifulvin; but, fortunately, 

 all these names have now disappeared, and the properties of the sub- 

 stances described under them by different observers, so far as they have 

 been substantiated, have been aggregated under one name and to one 

 substance, bilirubin, the red colouring matter of bile. Bilirubin is a con- 

 stant constituent of bile, and is found besides as a calcium compound in 

 red gall stones. It is also present in traces in the serum of some animals. 

 Hammarsten 2 found it in the serum of the horse. By precipitating 

 the serum globulin with acetic acid, the pigment is thrown down with 

 the globulin, and on drying the precipitate and extracting with chloro- 

 form, bilirubin is dissolved out. It seems, however, to be absent in 



1 Ztschr.f. physiol. Chem., Strassburg, 1889, Bd. xiv. S. 173. 



2 Jahresb. u. d. Fortschr. d. Thier-Chem., Wiesbaden, 1878, Bd. viii. S. 129. 



