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 oxyhemoglobin ; bilirubin (C 1( .H 18 N 2 3 ) on oxidation 
passes into biliverdin (C 1 i 6 H ls 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 bilif ulvin ; 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. physlol. Chem., Strassburg, 1889, Bd. xiv. S. 173. 
- Jokresb. ii. d. Fortschr. d. Thier-C'hem., Wiesbaden, 187S, Bd. viii. S. 129. 
