in the fixed principles of the egg during incubation. 399 
nish the phosphorus, entering as phosphoric acid, into the 
skeleton of the animal ; but that the earthy portion of the 
bones is derived from the transmutation of oil into lime can- 
not, perhaps, be safely asserted in the present state of the 
inquiry. 
With respect to the earthy matter found in the skeleton of 
the chick when it quits the shell, I think I can venture to assert, 
after the most patient and attentive investigation, that it does 
not pre-exist in the recent egg ; certainly not, at least in any 
known state. The only possible sources, therefore, whence it 
can be derived, are from the shell, or transmutation from 
other principles. 5 Whether it be actually derived from the 
shell, cannot be determined by chemistry ; because, as we 
have seen, the shells of different eggs differ so much, that 
the application of averages is out of the question ; and we are 
of course precluded from ascertaining the exact quantity of 
lime any particular shell originally contains. There are, 
however, very strong reasons for believing that the earthy 
matter is not derived from the shell. In the first place, the 
membrana putaminis never becomes vascular, and seems 
analogous to the epidermis ; hence the lime of the shell, which 
is exterior to this membrane, is generally considered by phy- 
siologists as extra-vascular ;* it is therefore extremely difficult 
behind in the yelk. In the present instance, however, the quantity of earthy matter 
was very minute : it had therefore disappeared, as well as the other principles of 
the yelk. When the chick is younger, the quantity of earthy matter is said to be 
piuch larger. Haller asserts that the yelk disappears about the 1 6th day; and 
Aristotle long ago remarked, that very little of it was left on the 10th day, after 
the chick had left the egg. 
* See an Essay “ on the connection between the vascular and extra-vascular parts 
of animals,” by Sir A. Carlisle. Thomson’s Annals, Vol. VI. p. 174. 
