94 
Colouring of the Shells of Birds' Eggs . [January, 
any mere mechanical exudation, but by some unknown phy- 
siological process of secretion, which breaks up the highly 
complex molecule of haemoglobin into one which can be 
formed artificially by heating it with strong sulphuric acid ; 
but in the living organism it combines with a second sub- 
stance differing from that with which it combines when the 
change is effedted by the adtion of hot strong sulphuric 
acid. Whether this view of the subjedt be in all respedts 
true or not, it at all events appears to me very plausible and 
well worthy of further examination, as pointing to the 
source of one of the most important colouring-matters of 
birds’ eggs. 
Relations of the Oocyans. 
In their normal condition the faeces of man, and probably 
those of many other animals, contain a yellow colouring- 
matter, which by oxidisation yields a substance closely 
related to, if not identical with, a produdt of the oxidisa- 
tion of the bilirubin of bile described by Jaffe* and by 
Heynsius and Campbell. t When extradted from faeces by 
alcohol without contadt with the air, it gives a spedtrum 
which cuts off the blue end without any definite band ; but 
when exposed to the air, or treated with some oxidising re- 
agent, the solution becomes orange-coloured, and the 
spedtrum shows a well-marked, dark, moderately broad 
absorption-band between the blue and the green, having its 
centre at wave-length 495 millionths of a millimetre. The 
addition of an excess of ammonia immediately removes this 
band without producing any well-marked change in the 
colour. Now I find, on comparing this substance with the 
produdt of the oxidisation of the two species of oocyan, 
which gives the spedtrum shown by Fig. 2, that there is a 
close agreement in general charadters, but yet a well-marked 
difference. The band in the produdt from the oocyans is 
about 5-4ths the breadth ; and its centre is a little farther from 
the blue end, being at wave-length 497 ; and caustic potash 
does not develop any band as in the other substances. On 
the whole, then, if we follow the same line of reasoning as 
that adopted in the case of oorhodeine, we are led to con- 
clude that the produdt of the oxidisation of the two kinds 
of oocyan is in some way connected with a produdt of the 
change and oxidisation of the colouring-matter of bile ; and 
thus we may perhaps be justified in concluding that there is 
* Virchow's Archiv., vol. xlvii., p. 262. 
f Pfluger’s Archiv., vol. iv., p. 520. 
