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 colli- quament, 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, how- ever, is certainly connected still more intimately with the albu- men 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 ex- ample will make this matter still more plain. There is an in- strument familiar to almost everybody, made rather for amuse- ment 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, cen- taurs 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
