Animal Substances being already assimilated, are more easily transmutable into other Animals, and therefore more nourishing than Vegetables; accordingly we find such Animals as are nourished by animal Food, to be more couragious, robust, active, bold, strong, than those which are nourished by Vegetables only. And even in Men, who have proper Organs for digesting both animal and vegetable Food, and consequently by Nature designed to use both, we find a remarkable Difference according to their Diet. The Inhabitants of fishing Towns, who may well be supposed to feed thereon, are strong, nervous and prolifick; and their Discharges, especially their Sweat, are often attended with a very strong rancid Smell. The Difference between these People, and some poor Peasants in the Country, who have no other than vegetable Food, is too obvious to mention.
As to the Preparation of animal Diet, by the Arts of Cookery, for Use, it is needless to repeat what was before said under this Head in relation to Vegetables, the Manner being pretty much the same. I shall only just observe, that in boiling, the Salts and a good Portion of Oyl is dissolved, and attenuated in the Decoction, which makes the Decoction it self very nourishing; the animal Substance it self is much relaxed and softned, so that it may almost all be reduced to a Jelly or thick Oyl; by roasting, the Salts are more brought into Action, and the fluid Parts lessened; so that what remains is more highly impregnated therewith; in baking no Part evaporates, but both Salts and Oyls are loosened and exalted by the Heat in the Oven; these Differences are observable by the Taste, affect the digestive Powers in different Degrees, and are usefully attended to, in many different Habits of the human Body, too tedious now to be enumerated.
It is to be observed here (as before concerning Vegetables) that the nearer the nutritious Juices are to their Roots, the more they partake of the Nature of their Origine; but the more they are mixed with animal Juices, and the greater Number of animal Circulations they pass through, the more they acquire an animal Nature. The Chyle in Animals feeding upon Vegetables is Acid, and generally speaking it is so in Men, because their Diet is more so than otherwise. The Milk is less Acid than the Chyle, but turns perfectly so by standing. In the Blood this Tendency is lost, and the Salts from fixed become volatile. But there are Juices in animal Bodies, that have Salts of a much higher Degree of Volatility than the Blood, but when they arrive at too high a state of Alkalescence, they are discharged generally by Urine, or some other Excretion.
I do not here pretend to account for these Facts; that they are such is beyond Controversy, and I think it very agreeable to the Order of Nature, that they should depend upon some general Cause: If the Principle of Attraction be one, and from what Sir Isaac Newton hath delivered in his Opticks it bids very fair for it, though that great Philosopher was either too modest, or too knowing, to propose it as such, otherwise than by way of Quære; if the Principle of Attraction be an universal Cause in such Effects as we have been speaking of, may it not very justly be supposed, that when animal Decoctions turn sowre by standing, and so far put on a vegetable Nature, as to differ from the Course animal Substances take, when left to themselves, that the Salts are disunited, and put from the Sphere of one anothers mutual Attraction, so as perhaps to exert a repelling Power; and may not the same thing happen, when putrified animal Substance becomes Nourishment for vegetable Bodies, their Salts being disunited, and their mutual Attractions dissolved or overcome by the Attraction of Water, Earth or other Parts, in the Substance which I before called vegetable Chyle? When Vegetables by Putrefaction acquire an animal Nature, are not the Salts brought into their Spheres of Attraction, so as to form different intestine Motions thereby, and to produce Heat, Fire, fetid Vapours, and Putrefaction?
Sir Isaac Newton, Opt. p. 362. compares a Particle of Salt to a Chaos, dense, hard, dry, and earthy in the Center; and rare, soft, moist and watry in the Circumference, and hence, says he, it seems to be that Salts are of a lasting Nature, being scarce destroyed unless by drawing away their watry Parts by Violence, or by letting them soak into the Pores of the central Earth, by a gentle Heat in Putrefaction, until the Earth be dissolved by the Water, and separated into smaller Particles, which by Reason of their smallness make the rotten Compound appear of a black Colour. Hence also it may be that the Parts of Animals and Vegetables preserve their several Forms, and assimilate their Nourishment; the soft and moist Nourishment easily changing its Texture by a gentle Heat and Motion, till it becomes like the dense, hard, dry, and durable Earth in the Center of each Particle. But when the Nourishment grows unfit to be assimilated, or the central Earth grows too feeble to assimilate it, the Motion ends in Confusion, Putrefaction and Death.
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.