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because it often begins or terminates with fomething which is not mechanical; that whenever it is intelligible and certain, it demonstrates intention and contrivance, as well in the works of nature as in thofe of art; and that it is the best demonstration which either can afford.

But, whilft I contend for thefe propofitions, I do not exclude myself from afferting that there may be, and that there are, other cafes, in which, although we cannot exhibit mechanism, or prove indeed that mechanism is employed, we want not fufficient evidence to conduct us to the fame conclufion.

There is what may be called the chymical part of our frame; of which, by reason of the imperfection of our chymistry, we can attain to no diftinct knowledge: I mean, not to a knowledge, either in degree or kind, fimilar to that which we poffefs of the mechanical part of our frame. It does not therefore afford the fame fpecies of argument as that which mechanifm affords; and yet it may afford an argument in a high degree fatiffactory. The gaftric juice, or the liquor which digefts the food in the ftomachs of animals, is of this clafs. Of all menftrua it is the most active, the most univerfal. In the human

ftomach,

ftomach, for instance, confider what a variety of strange fubftances, and how widely dif ferent from one another, it, in a few hours, reduces to one uniform pulp, milk, or mucilage. It feizes upon every thing, it diffolves the texture of almoft every thing, that comes in its way. The flesh of perhaps all animals ; the feeds and fruits of the greatest number of plants; the roots and ftalks and leaves of many, hard and tough as they are, yield to its powerful pervafion. The change wrought by it is different from any chymical folution which we can produce, or with which we are acquainted, in this refpect as well as many others, that, in our chymiftry, particular menftrua act only upon particular fubftances. Confider moreover that this-fluid, ftronger in its operation than a cauftic alkali or mineral acid, than red precipitate or aqua fortis itself, is nevertheless as mild, and bland, and inoffenfive to the touch or tafte, as faliva or gum water, which it much refembles. Confider, I fay, these feveral properties of the digestive organ, and of the juice with which it is fupplied, or rather with which it is made to fupply itself, and you will confefs it to be entitled to a name, which it has fometimes

received,

received, that of "the chymical wonder of animal nature.'

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Still we are ignorant of the composition of this fluid, and of the mode of its action; by which is meant that we are not capable, as we are in the mechanical part of our frame, of collating it with the operations of art. And this I call the imperfection of our chymistry; for, fhould the time ever arrive, which is not perhaps to be defpaired of, when we can compound ingredients, fo as to form a folvent, which will act in the manner in which the gastric juice acts, we may be able to af certain the chymical principles upon which its efficacy depends, as well as from what part, and by what concoction, in the human body, these principles are generated and derived.

In the mean time, ought that, which is in truth the defect of our chymistry, to hinder us from acquiefcing in the inference, which a production of nature, by its place, its properties, its action, its furprising efficacy, its invaluable use, authorizes us to draw in respect of a creative design?'

Another moft fubtle and curious func tion of animal bodies is fecretion.

This

function is semi-chymical and semi-mechani

cal;

cal; exceedingly important and diverfified in its effects, but obfcure in its procefs and in i's apparatus. The importance of the fecretory organs is but too well attefted by the difcafes, which an exceffive, a deficient, or a vitiated fecretion is almoft fure of producing. A fingle fecretion being wrong, is enough to make life miferable, or fometimes to deflroy it. Nor is the variety lefs than the importance. From one and the fame blood I fpeak of the human body) about twenty different fluids are separated; in their fenfible properties, in tafte, fmell, colour, and confiftency, the most unlike one another that is poffible? thick, thin, falt, bitter, fweet: and, if from our own we pass to other fpecies of animals, we find amongst their fecretions not only the most various, but the most opposite properties; the moft nutritious aliment, the deadlieft poison ; the sweetest perfumes, the moft fetid odours. Of thefe the greater part, as the gastric juice, the faliva, the bile, the flippery mucilage which lubricates the joints, the tears which moisten the eye, the wax which defends the ear, are, after they are fecreted, made ufe of in the animal economy; are evidently fubfervient, and are actually contributing to the

utilities

utilities of the animal itself. Other fluids seem to be separated only to be rejected. That this alfo is neceffary (though why it was originally neceffary, we cannot tell) is fhewn by the confequence of the feparation being long fufpended; which confequence is disease and death. Akin to fecretion, if not the fame thing, is affimilation, by which one and the fame blood is converted into bone, muscular flesh, nerves, membranes, tendons; things as different as the wood and iron, canvass and cordage, of which a fhip with its furniture is compofed. We have no operation of art wherewith exactly to compare all this, for no other reafon perhaps than that all operations of art are exceeded by it. No chymical elec tion, no chymical analysis or refolution of at fubftance into its conftituent parts, no mechanical fifting or divifion, that we are acquainted with, in perfection or variety come up to animal fecretion. Nevertheless the apparatus and process are obfcure; not to say, abfolutely concealed from our enquiries. In a few, and only a few inftances, we can difcern a little of the constitution of a gland. In the kidneys. of large animals we can trace the emulgent artery dividing itfelf into an infinite number

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