The Works of William Harvey M.D. / Translated from the Latin with a life of the author

by William Harvey

The chick too is made from the egg, as a man is made from a boy. For in the same way, as out of plants seeds arise, and out of seeds, buds, sprouts, stems, flowers, and fruits; so also out of the egg, the seed of the hen is produced, the dilatation of the cicatricula and the colliquament, the blood and the heart, as the first particle of the fœtus or fruit; and all this, in the same way as the day from the night, the summer from the spring, a man from a boy—one follows or comes after the other. So that, in the same way as fruits arise after flowers on the same stem, so likewise is the colliquament formed after the egg, the blood after this, as from the primogeneous humour, the chick after the blood, and out of it, as the whole out of a part; in the same way, as by Epicharmus’s exaggeration, out of calumnies comes cursing, and out of cursing fighting. For the blood first begins its existence with the punctum saliens, and at the same time, seems to be as well a part of the chick, and a kind of efficient or instrument of its generation, inseparable, as Fabricius thinks, from the agent. But how the egg may be called the efficient and instrument of generation, has partly been explained already, and will be illustrated more copiously by what we shall presently say.

So much has been fully established in our history, that the punctum pulsans and the blood, in the course of their growth, attach round themselves the rest of the body, and all the other members of the chick, just as the yelk in the uterus, after being evolved from the ovary, surrounds itself with the white; and this not without concoction and nutrition. Now the common instrument of all vegetative operations, is, in the opinion of all men, an internal heat or calidum innatum, or a spirit diffused through the whole, and in that spirit a soul or faculty of a soul. The egg, therefore, beyond all doubt, has its own operative soul, which is all in the whole, and all in each individual part, and contains within itself a spirit or animal heat, the immediate instrument of that soul. To one who should ask then, how the chick is made from the egg, we answer: after all the ways recited by Aristotle, and devised by others, in which it is possible for one thing to be made from another.

EXERCISE THE FORTY-FOURTH.

Fabricius is mistaken with regard to the matter of the generation of the chick in ovo.

As I proposed to myself at the outset, I continue to follow Fabricius as pointing out the way; and we shall, therefore, consider the three things which he says are to be particularly regarded in the generation of the chick, viz.: the agent, the matter, and the nourishment of the embryo. These must needs be all contained in the egg; he proposes various doubts or questions, and quotes the opinions of the most weighty authorities in regard to them, these opinions being frequently discordant. The first difficulty is in reference to the matter and nourishment of the chick. Hippocrates,[246] Anaxagoras, Alcmaeon, Menander, and the ancient philosophers, all thought that the chick was engendered from the vitellus, and was nourished by the albumen. Aristotle,[247] however, and after him, Pliny,[248] maintained, on the contrary, that the chick was incorporated from the albumen, and nourished by the vitellus. But Fabricius himself, will have it that neither the white nor yelk forms the matter of the chick; he strives to combat both of the preceding opinions, and teaches that the white and the yellow alike do no more than nourish the chick. One of his arguments, amongst a great number of others which I think are less to be acquiesced in, appears to me to have some force. The branches of the umbilical vessels, he says, through which the embryo undoubtedly imbibes its nourishment, are distributed to the albumen and the vitellus alike, and both of these fluids diminish as the chick grows. And it is on this ground, that Fabricius in confirmation of his opinion, says[249]: “Of the bodies constituting the egg, and adapted to forward the generation of the chick, there are only three, the albumen, the vitellus, and the chalazæ; now the albumen and vitellus are the nourishment of the chick; so that the chalazæ alone remain as matter from which it can be produced.”

Nevertheless, that the excellent Fabricius is in error here, we have demonstrated above in our history. For after the chick is already almost perfected, and its head and its eyes are distinctly visible, the chalazæ can readily be found entire, far from the embryo, and pushed from the apices towards the sides: the office of these bodies, as Fabricius himself admits, is that of ligaments, and to preserve the vitellus in its proper position within the albumen. Nor is that true, which Fabricius adds in confirmation of his opinion, namely, that the chalazæ are situated in the direction of the blunt part of the egg. For after even a single day’s incubation, the relative positions of the fluids of the egg are changed, the yelk being drawn upwards, and the chalazæ on either hand removed, as we have already had occasion to say.

He is also mistaken when he speaks of the chalazæ, as proper parts of the egg. The egg consists in fact but of white and yelk; the chalazæ as well as the membranes, are mere appendages of the albumen and vitellus. The chalazæ, in particular, are the extremities of certain membranes, twisted and knotted; they are produced in the same way as a rope is formed by the contortion of its component filaments, and exist for the purpose of more certainly securing the several elements of the egg in their respective places.

Fabricius, therefore, reasons ill when he says, that “the chalazæ are found in the part of the egg where the embryo is produced, wherefore it is engendered from them;” for even on his own showing, this could never take place, he admitting that the chalazæ are extant in either extremity of the egg, whilst the chick never makes its appearance save at the blunt end; in which, moreover, at the first commencement of generation, no chalaza can be seen. Farther, if you examine the matter in a fresh egg, you will find the superior chalaza not immediately under the blunt end or its cavity, but declined somewhat to the side; not to that side, however, where the cavity is extending, but rather to the opposite side. Still farther, from what has preceded, it is obvious that the relative positions of the fluids of the egg are altered immediately that incubation is begun: the eye increased by the colliquament is drawn up towards the cavity in the blunt end of the egg, whence the white and the chalaza are on either hand withdrawn to the side. For the macula or cicatricula which before incubation was situated midway between the two ends, now increased into the eye of the egg, adjoins the cavity in the blunt end, and whilst one of the chalazæ is depressed from the blunt end, the other is raised from the sharp end, in the same way as the poles of a globe are situated when the axis is set obliquely; the greater portion of the albumen, particularly that which is thicker, subsides at the same time, into the sharp end.

Neither is it correct to say, that the chalazæ bear a resemblance in length and configuration to the chick on its first formation, and that the number of their nodules corresponds with the number of the principal parts of the embryo; a statement which gives Fabricius an opportunity of adducing an argument connected with the matter of the chick, based on the similarity of its consistency to that of the chalazæ. But the red mass (which Fabricius regarded as the liver) is neither situated in nor near the chalaza, but in the middle of the clear colliquament; and it is not any rudiment of the liver but of the heart alone. Neither does his view square with the example he quotes of the tadpole, “of which,” he says, “there is nothing to be seen but the head and the tail, that is to say, the head and spine, without a trace of upper or lower extremities.” And he adds, “he who has seen a chalaza, and this kind of conception, in so far as the body is concerned, will believe that in the former, he has already seen the latter.” I, however, have frequently dissected the tadpole, and have found the belly of large size, and containing intestines and liver and heart pulsating; I have also distinguished the head and the eyes. The part which Fabricius takes for the head, is the rounded mass [or entire body] of the tadpole, whence the creature is called ‘gyrinus,’ from its circular form. It has a tail with which it swims, but is without legs. About the epoch of the summer solstice, it loses the tail, when the extremities begin to sprout. Nothing however occurs in the nature of a division of the embryo pullet into the head and spine, which should induce us to regard it as produced from the chalazæ, and in the same manner as the tadpole.

The position and fame of Fabricius, however, a man exceedingly well skilled in anatomy, do not allow me to push this refutation farther. Nor indeed, is there any necessity so to do, seeing that the thing is so clearly exhibited in our history.