Page:The Works of William Harvey (part 1 of 2).djvu/494

 already prepared, it is carried as nourishment for the chick ; still it is certain that the greater portion of the yelk remains after the disappearance of the albumen; that it is laid up in the abdomen of the chick when excluded, and, attracted or absorbed by the branches of the vena portse, that it is finally carried to the liver.

It is manifest, therefore, that the chick when hatched, is nourished by the yelk in the first period of its independent existence. And as within the egg the embryo was nourished partly by the albumen, partly by the vitellus, but principally by the albumen, which is both present in larger quantity, and is more speedily consumed, so when the chick is hatched, and when all the nourishment that is taken must pass through the liver to undergo ulterior preparation, is it nourished partly by the vitellus and partly by chyle absorbed from the intestines, but principally by chyle, which the host of subdivisions of the mesenteric vessels seize upon, whilst there is but a single vessel from the porta distributed to the vitellus, and by and by but little of it remains. Nature, therefore, acts as does the nurse, who gradually habituates her infant to the food which is to take the place of her failing supply of milk, The pullet is thus gradually brought from food of more easy to food of more difficult digestion, from yelk to chyle.

Wherefore there is every reason for what we perceive in connexion with the course of the veins in the egg. When the embryo first begins to be formed, they are distributed to the colliquament only, where the blood finds suitable nutriment and matter for the formation of the 'body ; but by and by they extend into the thinner albumen, whence the chick, whilst it is yet in the state of gelatine or mucor, and resembles a maggot in form, derives its increase ; the branches next extend into the thicker albumen, and then into the vitellus, that they may also contribute to the support of the foetus, which, having at length arrived at maturity and been extruded, still preserves a portion of the yelk (or milk) within its abdomen, whereby it is main- tained in part, in part by food selected and prepared for it by the mother, until it is able to look out for and to digest its own aliment. Thus does nature most wisely provide food through the whole round of generation, suited to the various strength of the digestive faculty in the future being. In the first period