Now these ideas are partly true, partly false. It is not true, for instance, that the embryo of the common fowl is first formed from the albumen and then nourished by the vitellus; for, from the history of the formation of the chick in ovo, from the course of the umbilical vessels and the distribution of their branches, which undoubtedly serve for obtaining nourishment, it obviously appears that the constituent matter, and the nu- triment are supplied to the chick from its first formation by the yelk, as well as the white ; the fluid which we have called the colliquament seems farther to be supplied, not less by the vitellus than the albumen ; a certain portion of both the fluids seems, in fact, to be resolved. And then the spot, by the ex- pansion of which the colliquament is formed in the first in- stance, and which we have called the eye, appears to be im- pressed upon the membrane of the vitellus.
The distinction into yellow and white, however, seems to be a thing necessary : these matters, as they are undoubtedly of different natures, appear also to serve different offices ; they are therefore completely separate in the perfect egg, one of them being more the other less immediately akin to proper alimentary matter ; by the one the foetus is nourished from the very beginning, by the other it is nourished at a later period. For it is certain, as Fabricius asserts, and as we afterwards maintain, that both of them are truly nutritious, the albumen as well as the vitellus, the albumen being the first that is con- sumed. I therefore agree with Aristotle against the physicians, that the albumen is the purer portion of the egg, the better concocted, the more highly elaborated; and, therefore, whilst the egg is getting perfected in the uterus, is the albumen as the hotter portion poured around in the circumference, the yelk or more earthy portion subsiding to the centre. For the albumen appears to contain the larger quantity of animal heat, and so to be nutriment of a more immediate kind. For like reasons it is probable that the albumen is purer and better concocted externally than it is internally.
When medical writers affirm that the yelk is the hotter and more nutritious portion of the egg, this I imagine is meant as it affords food to us, not as it is found to supply the wants of the chick in ovo. This, indeed, is obvious from the history of the formation of the chick, by which the thin albumen is ab-
