There is one animal Juice which deserves to be more particularly considered, not only because it is more used in our Food, than any other, but because it seems to partake of that just Medium between animal and vegetable Substances so desirable in our Diet, and that is Milk. It is neither Acid nor Alkaline; it seems to have enough of the animal Nature, to give strong and perfect Nourishment to animal Bodies, and to be easily assimilable to their Substance; enough of the Vegetable to prevent too strong a Tendency to a volatile Alkali; being a kind of Emulsion, or white, oily animal Liquor, prepared originally from Vegetables, and from which all the Parts of animal Bodies may receive their Nourishment and Growth. Many Persons have lived entirely upon Milk; and the Body of a Child may, at the End of some Months after its Birth, be considered as compounded of the Milk of its Nurse; the Parts it brought into the World being changed for others, supplied by the Nourishment. Tho’ Milk be of it self neither Acid nor Alkaline, it may not be amiss to take Notice of the Changes it undergoes upon being mixed with either, because hence we may determine its Agreement or Disagreement with different Constitutions. If Milk be mixed with Acids it coagulates into a Curd; if mixed with Alkalies, upon Heat it turns Yellow, then Red, and at length to a very deep dark Red, and by long continuance Black. Milk taken from Animals that feed upon Vegetables, if suffered to stand in a clean glass Vessel, will of it self separate into two Parts; the lighter, and more oily, rising to the Top in the Form of Cream; both which in a few Days turn sowre, and at the End of ten or twelve Days, acquire a very considerable Degree of Acidity; but if the Animal it be taken from feed upon animal Diet, or have fasted too long, or be feverish, or use strong Exercise; it will in these Cases have a brackish or saline Taste, which is a strong Evidence of its Tendency to Putrefaction, and accordingly instead of turning sowre, it will turn rancid, and run into an Ichor. It may fairly be concluded from hence, that Milk is not proper Food in acid Constitutions; for if Milk, upon the Mixture of Acids, turn into Curds and Whey, it is reasonable to expect, that if it be taken by Persons whose Bodies abound with Acids, it shall be separated into a thin serous Fluid, and a strong Coagulum; which turning grumous, may cause Obstructions in the _Viscera_, while it ceases to be mixed and diluted with the _Serum_, which instead of performing that Office, may go off in the Discharges of the Skin, or of Urine, leaving the Body pale, faint and weak; and hence may arise many chronical Distempers, foreign to our Purpose to enumerate.