364 MR. SORBY ON THE COLOURING OF BIRDS’ EGGS. [May 4, 
out the kind of arguments made use of in my late paper in the 
‘Monthly Microscopical Journal,’ the conclusions to which we are 
led by the above-described facts are that oorhodeine is in some way 
or other closely related to cruentine, but not identical with it, as 
shown not only by the well-marked difference in the spectra, but 
also by the difference in their solubility and power of resisting the 
decomposing action of powerful reagents. 
In the present state of our knowledge the most plausible expla- 
nation of all the facts is that perhaps oorhodeine and cruentine con- 
tain some common coloured radical of the same chemical or physical 
constitution, combined with some other substance which is itself 
colourless, and that this second constituent is not the same in oorho- 
deine as in cruentine, but differs sufficiently to modify the general 
properties and to slightly alter the size of the ultimate molecules and 
so as to cause them to be related to waves of light of a little diffe- 
rent length. It must, however, be borne in mind that I advance 
these views merely as being the most probable explanation of the 
facts. Assuming them to be true, they lead to the conclusion that 
the oorhodeine of birds’ eggs is derived from the red colouring~ 
matter of the blood, not by any mere mechanical exudation, but by 
some unknown physiological process of secretiun, which breaks up 
the highly complex molecule of heemogtobin into one which can be 
formed artificially by heating it with strong sulphuric acid ; but in 
the living organism it combines with a second substance differing 
from that with which it combines when the change is effected by 
the action of hot strong sulphuric acid. Whether this view of the 
subject be in all respects 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 feeces of man, and probably those of 
many other animals, contain a yellow colouring-matter, which by 
oxidization yields a substance closely related, if not identical, with 
a product of the oxidization of the bilirubin of bile described by 
Jaifé* and by Heynsius and Campbell+. When extracted from 
feeces by alcohol without contact with the air, it gives a spectrum 
which cuts off the blue end without any definite band; but when 
exposed to the air or treated with some oxidizing reagent, the 
solution becomes orange-coloured, and the spectrum 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 
product of the oxidization of the two species of oocyan, which 
gives the spectrum shown by fig. 2, that there is a close agreement 
in general characters, but yet a well-marked difference. The band 
* Virchow’s Archiv, vol. xlvii. p. 262. + Pfliiger’s Archiv, vol. iv. p. 520. 
