Dr John Davy on the Hgqs of Birds. 253 
attribute, not to any mineral colouring matter, but to an 
organic or animal colouring matter, and that, in part at 
least, connected with molecular arrangment, analogous to 
what is witnessed in flowers. As examples, I may give the 
results of the examination I have made of the dark-brown, 
almost black, colouring matter of the egg of the common 
grouse, and of the green of the egg of the starling, and of 
the green with dark-brown spots, these, too, almost black, 
of the common thrush. Of all these, the colouring matter 
has been destroyed before the blowpipe, the shell being 
rendered perfectly white. In the instance of the thrush’s, 
it is remarkable that, after incandescence, in cooling it re- 
covers in a slight degree its greenish hue, and yet loses it 
when quite cold; a circumstance this favourable to the idea 
of the colour, as before remarked, depending in part on 
molecular arrangement. The green of neither of the eggs 
is altered by the weak acids, nor by solutions of the alkalies. 
In strong nitric acid it changes to yellow. In strong 
muriatic acid it resists change for many hours, fading and 
disappearing under the continued action of the acid. Chlo- 
rine has a similar effect; and bright sunshine, after many 
days exposure, renders it fainter: sulphurous acid does not 
bleach it. On the colour of the grouse’s egg strong muriatic 
acid has no perceptible effect; strong nitric acid changes 
it to a light dirty yellow. That the colour of this egg is 
not in any way owing to the presence of iron seemed-to be 
indicated by the following experiment :—A minute portion 
of blood was applied to the shell; on exposure to the blow- 
pipe, the spot was marked by a slight ochrey stain, the 
cloured portions becoming, after the destruction of the 
animal matter, quite white. 
The contents, the albumen and yolk, of the several kinds 
of eggs, though so very similar, are found, even on slight 
examination, to have points of difference. I shall now re- 
strict myself to three,—viz., the proportional weight of the 
albumen and yolk, including the shell and its membranes ; 
the density of the two, or rather the proportion of solid 
matter which each afforded after the dissipation of their 
aqueous portion by thorough drying; and the effects of 
heat and its degree in producing the coagulation of the 
NEW SERIES,—VOL. XVIII. NO. 11.—ocToBerR 1863. 2K 
