86 Colouring of the Shells of Birds' Eggs. [January, 
effect on the general colour than to make it somewhat more 
dull. Since the entire spedtrum is not accurately known, I 
will merely give the position of the different very narrow 
absorption-bands in millionths of millimetres of wave-length. 
The most complete spedtrum shows three bands. On adding 
excess of ammonia, that nearest the red end alone remains, 
whilst the addition of a small excess of a strong acid removes 
all but the central band — and when the excess is consider- 
able, raises this band towards the blue end. These fadts 
will be better shown by the following table : — 
Centre of bands. 
Most complete spedtrum . . . 668 648 628 
With excess of ammonia. . . 668 — — 
With a little acid — 643 — 
With much acid — 641 — - 
By means of these bands a very small quantity of this 
substance can easily be recognised. It is not readily de- 
composed — but, when adted upon with oxidising reagents, 
may be changed into another colouring-matter, giving rise 
to a spedtrum with one or two somewhat obscure bands. 
7. Lichno xanthine. — In my paper on comparative vegetal 
chromatology, I have described a substance which occurs 
in greater or less amount in almost all classes of plants, 
from the lowest to the highest, but is more especially abun- 
dant in and charadteristic of lichens and fungi, and for this 
reason has been named by me lichno xanthine. The spedtrum 
shows strong general absorption of the blue end down to 
about wave-length 510 millionths of a millimetre, and a much 
weaker general absorption down to about 590 millionths. 
Acids and alkalies produce very little change ; and it is very 
slowly altered by strong oxidising reagents. I have been 
able to prepare it artificially by the decomposition of resins. 
Some such substance is undoubtedly present in small 
quantity in very many kinds of birds’ eggs ; and occasionally 
there is so much as to materially modify the general colour. 
It may occasionally have been, to some extent, derived from 
the decayed vegetable matter of the nest, or, in the case of 
eggs which have been kept long, may be partly due to the 
growth of minute fungi ; but, at the same time, a very closely 
allied, if not identical, substance does really appear to be a 
normal constituent of the shell of eggs having a peculiar 
brick-red colour. Very probably it may not be formed in the 
animal organism, but absorbed diredtly from the vegetable 
food of the birds. This need not in any way surprise us, 
since it is a substance of great stability, and there is strong 
