There is one consideration in the whole question, however, which is sorely against him; it is this—how is the blood formed in the egg? by what agent is either white or yelk turned into blood whilst the liver is not yet in existence? For in the egg, at all events, he could not say that the blood was transfused from the mother. He says, indeed, “This blood is produced and concocted in the veins rather than in the liver; but it becomes bone, cartilage, flesh, &c. in the parts themselves, where it undergoes exact concoction and assimilation.” In this he adds nothing; he neither tells us how or by what means perfect blood is concocted and elaborated in the minute veins both of the albumen and vitellus, the liver, as I have said, not having yet come into existence,—not a particle of any part of the body, in fact, having yet been produced by which either concoction or elaboration might be effected. And then, forgetful of what he has previously said, viz. that the hot and hæmatous parts are nourished by the vitellus and the cold and anæmic parts by the albumen, he is plainly in contradiction with himself when he admits that the same blood is turned into bone, cartilage, flesh, and all other parts.
More than this, Fabricius has slipped the greatest difficulty of all, the source of not a little doubt and debate to the medical mind, viz. how the liver should be the source and artificer of the blood, seeing that this fluid not only exists in the egg before any viscus is formed, but that all medical writers teach that the parenchymata of the viscera are but effusions of blood? Is the work the author of its workman? If the parenchyma of the liver come from the blood, how can it be the cause of the blood?
What follows is of the same likelihood: “There is another reason wherefore the albumen should be separated from the yelk, namely, that the fœtus may swim in it, and be thus supported, lest tending downwards by its own weight, it should incline to one particular part, and dragging, should break the vessels, in preventing which the viscidity and purity of the albumen contribute effectually. For did the fœtus grow amid the yelk, it might readily sink to the bottom, and so cause laceration of that body.” Sufficiently jejune! For what, I entreat, can the purity of the albumen contribute to the support of the embryo? Or how should the thinner albumen sustain it better than the thicker and more earthy yelk? Or where the danger, I ask, of its sinking down, when we see that the egg in incubation is always laid on its side, and there is nothing to fear either for the ascent or the descent of the embryo? It is indubitable, indeed, that not only does the embryo of the chick float in the egg, but that the embryo of every animal during its formation floats in the uterus; this however takes place amidst the fluid which we have called colliquament, and neither in the albumen nor vitellus, and we have elsewhere given the reason wherefore this is so.
“Aristotle informs us,” says Fabricius, “that the vitellus rises to the blunt end of the egg when the chick is conceived; and this because the animal is incorporated from the chalaza, which adheres to the vitellus; whence the vitellus which was in the middle is drawn towards the upper wider part of the egg, that the chick may be produced where the natural cavity exists, which is so indispensable to its well-being.” The chalaza, however, is certainly connected still more intimately with the albumen than with the yelk.
My mode of interpreting the ascent in question is this: the spot or cicatricula conspicuous on the membrana vitelli, expands under the influence of the spirituous colliquament engendered within it, and requiring a larger space, it tends towards the blunt end of the egg. The liquefied portion of the vitellus and albumen, diluted in like manner, and concocted and made more spirituous, swims above the remaining crude parts, just as the inferior particles of water in a vessel, when heated, rise from the bottom to the top, a fact which every medical man must have observed when he had chanced to put a measure of thick and turbid urine into a bath of boiling water, in which case the upper part first becomes clear and transparent. Another example will make this matter still more plain. There is an instrument familiar to almost everybody, made rather for amusement than any useful purpose, nearly full of water, on the surface of which float a number of hollow glass beads which by their lightness and swimming together support a variety of figures, Cupids with bows and quivers, chariots of the sun, centaurs armed, and the like, which would else all sink to the bottom. So also does the eye of the egg, as I have called it, or first colliquament, dilated by the heat of the incubating fowl and genital virtue inherent in the egg, expand, and thereby rendered lighter, rise to the top, when the vitellus, with which it is connected follows. It is because the cicatricula, formerly situated on the side of the vitellus, now tends to rise directly upwards that the thicker albumen is made to give place, and the chalazæ are carried to the sides of the egg.
EXERCISE THE SIXTY-FIRST.
Of the uses of the other parts of the egg.
The shell is hard and thick that it may serve as a defence against external injury to the fluids and the chick it includes. It is brittle, nevertheless, particularly towards the blunt end, and as the time of the chick’s exclusion draws near, doubtless that the birth may suffer no delay. The shell is porous also; for when an egg, particularly a very recent one, is dressed before the fire, it sweats through its pores. Now these pores are useful for ventilation; they permit the heat of the incubating hen to penetrate more readily, and the chick to have supplies of fresh air; for that it both breathes and chirps in the egg before its exclusion is most certain.
The membranes serve to include the fluids, and therefore are they present in the same number as these, and therefore is the colliquament also invested, as soon as it is produced, with a tunica propria, which Aristotle[322] refers to in these words: “A membrane covered with ramifications of blood-vessels already surrounds the clear liquid,” &c. But the exit of the chick being at hand, and the albumen and colliquament being entirely consumed, all the membranes, except that which surrounds the vitellus, are dried up and disappear; the membrana vitelli, on the contrary, along with the yelk, is retracted into the peritoneum of the chick and included in the abdomen. Of the membranes two are common to the whole egg, which they surround immediately under the shell; the rest belong, one to the albumen, one to the yelk, one to the colliquament; but all still conduce to the preservation and separation of the parts they surround. The outer of the two common membranes which adheres to the shell is the firmer, that it may take no injury from the shell; the inner one again is smooth and soft, that it may not hurt the fluids; in the same way, therefore, as the meninges of the brain protect it from the roughness of the superincumbent skull. The internal membranes, as I have said, include and keep separate their peculiar fluids, whence they are extremely thin, pellucid, and easily torn.
Fabricius ascribes great eminence and dignity to the chalazæ, regarding them as the parts whence the chick is formed; he, however, leaves the spot or cicatricula connected with the membrana vitelli without any office whatsoever, looking on it merely as the remains of the peduncle whence the vitellus was detached from the vitellarium in the superior uterus of the hen. In his view the vitellus formerly obtained its nourishment either by this peduncle or the vessels passing through it; but when detached, and no longer nourished by the hen, a simple trace of the former connexion and important function alone remains.