Page:The Works of William Harvey (part 1 of 2).djvu/437

 which, in the course of growth, has at one and the same time dis- tinct structures formed and its figure established, and acquires an additional birth of parts afterwards, each in its own order ; in the same way, for instance, as the bud bursting from the top of the acorn, in the course of its growth, has its parts separately taking the form of root, wood, pith, bark, boughs, branches, leaves, flowers, and fruit, until at length out comes a perfect tree ; just so is it with the creation of the chick in the egg : the little cicatrix, or small spot, the foundation of the future structure, grows into the eye and is at the same time sepa- rated into the colliquament ; in the centre of which the punctum sanguineum pulsans commences its being, together with the ramification of the veins ; to these is presently added the nebula, and the first concretion of the future body; this also, in proportion as its bulk increases, is gradually divided and distinguished into parts, which however do not all emerge at the same time, but one after the other, and each in its proper order. To conclude, then : in the generation of those animals which are created by epigenesis, and are formed in parts, (as the chick in the egg,) we need not seek one material for the incorporation of the foetus, another for its commencing nutrition and growth ; for it receives such nutrition and growth from the same material out of which it is made ; and, vice versa, the chick in the egg is constituted out of the materials of its nutrition and growth. And an animal which is capable of nutrition is of the same potency as one which is augmenta- tive, as we shall afterwards show; and they differ only, as Aristotle says, in their distinctness of being; in all other respects they are alike. For, in so far as anything is convertible into a sub- stance, it is nutritious, and under certain conditions it is augmen- tative : in virtue of its repairing a loss of substance, it is called nutriment, in virtue of its being added, where there is no such loss of substance, it is called increment. Now the material of the chick, in the processes of generation, nutrition, and aug- mentation is equally to be considered as aliment and incre- ment. We say simply that anything is generated, when no part of it has pre-existed; we speak of its being nourished and growing when it has already existed. The part of the foetus which is first formed is said to be begotten or born ; all sub- stitutions or additions are called adnascent, or aggenerate.

22