From the above, it clearly appears that Aristotle recognizes a certain order and commencement in animal generation, namely, the heart, which he regards as the first produced and first vivified part of the animal, and, like a son set free from the tutelage of his parents, as self-sufficing and independent, whence not only does the order of the parts proceed, but as that by which the animal itself is maintained and preserved, receiving from it at once life and sustenance, and everything needful to the perfection of its being. For as Seneca says:[293] “In the semen is comprised the entire cause of the future man; and the unborn babe has written within it the law of a beard and a hoary head. For the whole body and the load of future years are already traced in delicate and obscure outlines in its constitution.”
We have already determined whether the heart were this primigenial part or not; in other words, whether Aristotle’s words refer to that part which, in the dissection of animals, is seen sooner than all the rest, the punctum saliens, to wit, with its vessels full of blood; and we have cordially assented to an answer in the affirmative. For I believe that the blood, together with its immediate instruments, the umbilical vessels, by which, as by roots, nutriment is attracted, and the pulsating vesicles, by which this nutriment is distributed, to maintain life and growth in every other part, are formed first and foremost of all. For as Aristotle[294] has said, it is the same matter by which a thing grows, and by which it is primarily constituted.
Many, however, err in supposing that different parts of the body require different kinds of matter for their nourishment. As if nutrition were nothing more than the selection and attraction of fit aliment; and in the several parts of the body to be nourished, no concoction, assimilation, apposition, and transmutation were required. This as we learn, was the opinion of Anaxagoras of old:
Who held the principles of things to be
Homœomeric:—bone to be produced
Of small and slender bones; the viscera
Of small and slender viscera; the blood
Of numerous associate drops of blood.[295]
But Aristotle,[296] with the greatest propriety, observes: “Distinction of parts is not effected, as some think, by like being carried by its nature to like; for, besides innumerable difficulties belonging to this opinion in itself, it happens that each similar part is severally created; for example, the bones by themselves, the nerves, the flesh, &c.” But the nourishment of all parts is common and homogeneous, such as we see the albumen to be in the egg, not heterogeneous and composed of different parts. Wherefore all we have said of the matter from which parts are made, is to be stated of that by which they increase: all derive nourishment from that in which they exist in potentia, though not in act. Precisely as from the same rain plants of every kind increase and grow; because the moisture which was a like power in reference to all, becomes actually like to each when it is changed into their substances severally: then does it acquire bitterness in rue, sharpness in mustard, sweetness in liquorice, and so on.
He explains, moreover, what parts are engendered before others, and assigns a reason which does not differ from the second basis of Fabricius. “The cause by which, and the cause of this cause, are different; one is first in generation, the other in essence;” by which we are to understand that the end is prior in nature and essence to that which happens for the sake of the end; but that which happens for the sake of the end must be prior in generation. And on this ground Fabricius rightly infers that all those parts which minister to the vegetative principle, are engendered before those that serve the sensitive principle, inasmuch as the former is subordinate to the latter.
He subsequently adds the differences of those parts which are made for some special purpose: some parts, for example, are instituted for a purpose by nature, because this purpose ensues; and others because they are instruments which the purpose employs. The former he designates genitalia, the latter instrumenta. For the end or purpose, he says, in some cases, is posterior, in others prior to that which is its cause. For both the generator and the instruments it uses must exist anteriorly to that which is engendered by or from them. The parts serving the vegetative principle, therefore, are prior to the parts which are the ministers of sense and motion. But the parts dedicated to motion and sensation are posterior to the motive and sensitive faculties, because they are the instruments which the motive and sensitive faculties employ. For it is a law of nature that no parts or instruments be produced before there be some use for them, and the faculty be extant which employs them. Thus there is neither any eye nor any motive organ engendered until the brain is produced, and the faculties preexist which are to see and to govern motion.
In like manner, as the pulsating vesicles serve as instruments for the motion of the blood, and the heart in its entire structure does the same, (as I have shown in the work on the Motion of the blood,) urging the blood in a ceaseless round through every part of the body, we see that the blood must exist before the heart, both in the order of generation and of nature and essence. For the blood uses the heart as an instrument, and moreover, when engendered it continues to nourish the organ by means of the coronary arteries, distributing heat, spirits, and life to it through their ramifications.
We shall have further occasion to show from an entire series of anatomical observations, how this rule of Aristotle in respect of the true priority of the parts is borne out. Meantime we shall see how he himself succeeds in duly inferring the causes of priority in conformity with his rule.
“After the prime part—viz. the heart—is engendered,” he says, “the internal parts are produced before the external ones, the superior before the inferior; for the lower parts exist for the sake of the superior, and that they may serve as instruments, after the manner of the seeds of vegetables, which produce roots sooner than branches.”