Aristotle[175] appears to have known this dissolved fluid, when he says: “A membrane, too, marked with sanguineous fibres, surrounds the white fluid at this time (the third day), arising from those orifices of the veins.” Now the philosopher can neither be supposed by the words “white fluid,” to refer to the albumen at large, because at this period the membrane of the white is not yet covered with veins; it is only the membrane of the dissolved fluid which appears with a few branches of veins distributed over it here and there. And because he says: “this membrane, too,” as if he understood another than those which he had spoken of as investing the albumen and the yelk before incubation, and designated this one as first arising after the third day, and from the orifices of the veins.
Coiter seems also to have known of this dissolved fluid; he says: “A certain portion of the albumen acquiring a white colour, another becoming thicker.” The fluid in question is surrounded with its proper membrane, and is distinct and separate from the rest of the albumen before there is any appearance of blood. We shall have occasion, by and by, to speak of the singular importance of this fluid to the fœtuses of every animal. Whilst they float in it they are safe from succussion and contusion, and other external injury of every kind; and they moreover are nourished by it. I once showed to their serene majesties the king and queen, an embryo, the size of a French-bean, which had been taken from the uterus of a doe; all its membranes were entire, and from its genital organs we could readily tell that it was a male. It was, in truth, a most agreeable natural spectacle; the embryo perfect and elegant, floating in this pure, transparent, and crystalline fluid, invested with its pellucid tunica propria, as if in a glass vessel of the greatest purity, of the size of a pigeon’s egg.
EXERCISE THE SEVENTEENTH.
The third inspection of the egg.
Having seen the second process or preparation of the egg, towards the production of the embryo which presents itself in the course of the third day, we proceed to the Third Stage, which falls to be considered after the lapse of three days and as many nights. Aristotle[176] says: “Traces of generation commence in the egg of the hen after three days and three nights [of incubation];” for example, on Monday morning, if in the morning of the preceding Friday the egg has been put under the hen. This stage forms the subject of the third figure in Fabricius.
If the inspection of the egg be made on the fourth day, the metamorphosis is still greater, and the change likewise more wonderful and manifest with every hour in the course of the day. It is in this interval that the transition is made in the egg from the life of the plant to the life of the animal. For now the margin of the diffluent fluid looks red, and is purpurescent with a sanguineous line, and nearly in its centre there appears a leaping point, of the colour of blood, so small that at one moment, when it contracts, it almost entirely escapes the eye, and again, when it dilates, it shows like the smallest spark of fire. Such at the outset is animal life, which the plastic force of nature puts in motion from the most insignificant beginnings!
The above particulars you may perceive towards the close of the third day, with very great attention, and under favour of a bright light (as of the sun), or with the assistance of a magnifying glass. Without these aids you would strain your eyes in vain, so slender is the purple line, so slight is the motion of the palpitating point. But at the beginning of the fourth day you may readily, and at its close most readily, perceive the “palpitating bloody point, which already moves,” says Aristotle, “like an animal, in the transparent liquid (which I call colliquamentum); and from this point two vascular branches proceed, full of blood, in a winding course” into the purpurescent circle and the investing membrane of the resolved liquid; distributing in their progress numerous fibrous offshoots, which all proceed from one original, like the branches and twigs of a tree from the same stem. Within the entering angle of this root, and in the middle of the resolved liquid, is placed the red palpitating point, which keeps order and rhythm in its pulsations, composed of [alternate] systoles and diastoles. In the diastole, when it has imbibed a larger quantity of blood, it becomes enlarged, and starts into view; in the systole, however, subsiding instantaneously as if convulsed by the stroke, and expelling the blood, it vanishes from view.
Fabricius depicts this palpitating point in his third figure; and mistakes it—a thing which is extraordinary—for the body of the embryo; as if he had never seen it leaping or pulsating, or had not understood, or had entirely forgotten the passage in Aristotle. A still greater subject of amazement, however, is his total want of solicitude about his chalazæ all this while, although he had declared the rudiments of the embryo to be derived from them.
Ulyssus Aldrovandus,[177] writing from Bologna nearly at the same time, says: “There appears in the albumen, as it were, a minute palpitating point, which The Philosopher declares to be the heart. And I have unquestionably seen a venous trunk arising from this, from which two other branches proceeded; these are the blood-vessels, which he says extend to either investing membrane of the yelk and white. And I am myself entirely of his opinion, and believe these to be veins, and pulsatile, and to contain a purer kind of blood, adapted to the production of the principal parts of the body, the liver, to wit, the lungs, and others of the same description.” Both of the vessels in question, however, are not veins, neither do they both pulsate; but one of them is an artery, another a vein, as we shall see by and by, when we shall farther show that these passages constitute the umbilical vessels of the embryo.
Volcher Coiter has these words: “The sanguineous point or globule, which was formerly found in the yelk, is now observed more in the albumen, and pulsates distinctly.” He says, erroneously, “formerly found in the yelk;” for the point discovered in the vitellus is white, and does not pulsate; nor does the sanguineous point or globe appear to pulsate at the end of the second day of incubation. But the point which we have indicated in the middle of the circle, and as constituting its centre in connexion with the vitellus, disappears before that point which is characterized by Aristotle as palpitating, can be discerned; or, as I conceive, having turned red, begins to pulsate. For both points are situated in the centre of the resolved fluid, and near the root of the veins which thence arise; but they are never seen simultaneously: in the place of the white point there appears a red and palpitating point.