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Proceedings of Royal Society of Edinburgh . [sess- 
by the light in twenty hours. In the dark chamber they 
began slowly to undergo change at the bottom of the tube 
after twenty-four hours. 
(d) A film of bile about 1 millimetre thick was dried at a low tem- 
perature. On the fourth day it had completely changed its 
colour to brown ; while, on the other hand, a film, similarly 
prepared, but kept in the dark, remained blue-green, the 
original colour of the bile, for a year and a-half — the time 
when it was finally examined. 
It would seem, therefore, that biliverdin readily parts with its 
oxygen like oxyhemoglobin. It is reduced in the sterilised tubes 
to bilirubin, but no further. This reduction is hastened by light, 
and putrefaction, and the presence of thick mucus. It is only pre- 
vented by drying the bile and keeping it in a dark chamber. 
When bile putrefies, or when, without putrefaction, the bile has 
been altered by boiling it, the bilirubin finally disappears, and no 
play of colour is obtained by the application of Gmelin’s test. 
This residue contained a brown pigment giving no absorption 
bands, and differing from hydrobilirubiu in its solubilities. It was 
insoluble in ether, but readily soluble in alcohol. 
Appendix. 
On the Reduction and Oxygenation of Pigments in the Bilirubin 
Series. 
Bilirubin, when exposed to the air, under ordinary circumstances, 
never becomes converted into biliverdin. This takes place, how- 
ever, if the solution has previously been rendered strongly alkaline 
by the addition of caustic soda solution. Both nascent oxygen and 
ozone, we find, are capable of effecting this change in bile of normal 
reaction. To do this experiment, pieces of blotting-paper soaked in 
bile should be exposed to the vapour of ozone ; ozonic ether, liberat- 
ing nascent oxygen, can also oxidise these papers. If human bile 
is poured into a small beaker, and a stream of electricity passed 
through it, obtained from some five or six Grove cells — the ter- 
minals should be of platinum — the oxygen given off from the 
positive terminal, in the course of three or four minutes, changes 
the bile in its vacinity, first to a green, and finally to a blue-green 
