Page:The Works of William Harvey (part 1 of 2).djvu/335

 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 1 says : " Traces of generation commence in the egg of the hen after three days and three nights [of in- cubation] ;" 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 pur- purescent 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, Avhen 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 insig- nificant 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 magni- fying 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 "palpi- tating bloody point, which already moves," says Aristotle, " like an animal, in the transparent liquid (which I call colliqua- meiitum); 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

1 Hist. Anira. lib. vi, cap. 3.