SECT. 2.
In order to be fully satisfied of the Nature of Milk, it is necessary to examine into the Manner of its Generation: It seems reasonable to imagine, that the Chyle, once received into the lacteal Vessels, and at length mixed with the Blood, is never again let forth with the same Appearance; only in Women at the Time of Childbirth, when it is plentifully separated, through the Ramifications of the Arteries, by the conglomerate Glands of the Breast. There is evidently a great Agreement between the Milk and the Chyle, in as much as the Chyle consists of a watry, limpid and gelatinous Fluid, with oily or fat Globules swimming therein. These Globules are pellucid, and differ both in Size and Figure; the Reason of its Whiteness is to be imputed to this: The oily Globules are mixed with the watry ones, in such Manner that several very smooth Globules are formed, which reflecting the Rays of Light in right Lines, occasion a white Colour; the same thing is observable in making Emulsions with oily Seeds, or upon mixing resinous Essences with Water, or mixing Oyl and Water, and shaking them well together; in these Cases, the watry and oily Particles, being thoroughly mixed, occasion such a Superficies as reflects a white Colour. Bolin, and several Authors have proved, that the Milk is no other than oily or fat Lymph or Chyle, brought with the Blood to the Breasts, and there deposited in the milky Cells. Berger hath very well explained the Manner of its Separation in the Breasts. The whole Substance of the Breasts, in Women giving Suck, is made up of various Ramifications of Arteries, from the thoracick and mamillary Arteries, which terminate in oval Cells, or glandulary Follicles; from hence the Breast swells with many milky Vessels, terminating in the Nipple; through these the more oily and chylous Parts of the Blood are derived from the Glands, where it is not only separated, and received, but gathered and preserved, while the remaining Mass of the Blood is returned by the Veins and Lymphaticks. These milky Rivulets, after breaking very small from the Ramifications of the Arteries, flow together into several larger Trunks, which in their Progress are united by Insertions of their Parts, in some Places more dilated, in others streightned, from several Cells and Cisterns, where the Milk is gathered and preserved, so as always to have a sufficient Quantity for the Nourishment of the Infant. Lastly, as the Chyle is separated from the Mass of the Food in the Bowels, not by any Precipitation, but by Percolation only; and as in the making of Emulsions, the oily Seeds communicate an oily Milkiness to the Water, and is separated from the grosser Parts by the Sieve, without the Intervention of any precipitating Medicine, so the chylous Juice is separated in the Bowels by gentle Pressure or the Peristaltick Motion, and strained through the Orifices of the lacteal Vessels, to be thence thrown into the Mass of the Blood. In like manner, the Milk is barely separated, by straining the milky Particles from the Blood, through the small Ramifications of the Arteries in the Glands of the Breasts.