304 ON GENERATION. 



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- 



