Page:The Works of William Harvey (part 1 of 2).djvu/333

 clear diffluent fluid, whether I should regard it as the innate heat, or radical moisture ; as a matter prepared for the future foetus, or a perfectly-concocted nourishment, such as dew is held to be among the secondary humours. For it is certain, as shall be afterwards shown, that the earliest rudiments of the foetus are cast in its middle, that from this the chick derives its first nutriment, and even when of larger size continues to live amidst it.

This solution therefore increases rapidly in quantity, par- ticularly in its internal region, which, as it expands, forces out and obliterates the external regions. This change is effected in the course of a single day, as is shown in the second figure of Fabricius. It is very much as it is with the eyes of those animals which have a very ample pupil, and see better by night than by day, such as owls, cats, and others, whose pupils expand very much in the dusk and dark, and, on the contrary, contract excessively in a brilliant light : one of these animals being taken quickly from a light into a shady place, the pupil is seen to enlarge in such wise that the coloured ring, called the iris, is very much diminished in size, and indeed almost entirely dis- appears.

Parisanus, falling upon these regions, is grossly mistaken when he speaks of " a honey-coloured, a white, a gray, and an- other white circle ;" and says that " the foetus is formed from the white middle point " (which, indeed, appears in these regions), and that " this is the semen of the cock." That he may exalt himself on a more notable subtlety he continues : " Before any redness is apparent in the body of the foetus, two minute vesicles present themselves in it; in the beginning, however, neither of them is tinged with red ;" one of these he would have us receive as the heart, the other as the liver. But in truth there is neither any vesicle present sooner than the redness of the blood is disclosed; nor does the embryo ever sud- denly become red in the course of the first days of its existence; nor yet does any of these vesicles present us with a trace of the liver. Both of them belong, in fact, to the heart, prefiguring its ventricles and auricles, and palpitating, as we shall after- wards show, they respond reciprocally by their systoles and diastoles.