viviparous animals are developed, and at the same time de- monstrate that these all derive their origin from eggs, and live by a twofold albuminous food in the womb. One of these is thinner, and contained within the ovum or conception; the other is obtained by the umbilical vessels from the placenta and uterine cotyledons. The fluid of the ovum resembles a dilute albumen in colour and consistence ; it is a sluggish, pellucid liquid, in all respects similar to that which we have called the colliquament of the egg, in which the embryo swims, and on which it feeds by the mouth. The fluid which the foetus obtains from the uterine placenta by the aid of the um- bilical vessels is more dense and mucaginous, like the inspis- sated albumen. Whence it clearly appears that the foetus in utero is no more nourished by its parent's blood than is the suckling afterwards, or the chick in ovo ; but that it is nou- rished by an albuminous matter concocted in the placenta, and not unlike white of egg.
Nor is the contemplation of the Divine Providence less useful than delightful when we see nature, in her work of evolving the foetus, furnishing it with sustenance adapted to its varying ages and powers, now more easy, by and by more difficult of digestion. For as the foetus acquires greater powers of digesting, so is it supplied with food that is successively thicker and harder. And the same thing may be observed in the milk of animals generally : when the young creature first sees the light the milk is thinner and more easy of concoction ; but in the course of time, and with increased strength in the suckling, it becomes thicker, and is more abundantly stored with caseous matter. Those flabby and delicate women, there- fore, who do not nurse their own children, but give them up to the breast of another, consult their health indifferently ; for mercenary nurses being for the major part of more robust and hardy frames, and their milk consequently thicker, more caseous, and difficult of digestion, it frequently happens that milk of this kind given to the infants of such parents, parti- cularly during the time of teething, is not well borne, but gives rise to crudities and diarrhoeas, to griping, vomiting, fever, epilepsy, and other formidable diseases of the like nature.
What Fabricius says, 1 and strives to bolster up by certain
1 Op. cit. p. 34.
