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because it often begins or terminates with something 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 those of art; and that it is the best demonstration which either can afford.
But, whilst I contend for these propositions, I do not exclude myself from asserting that there may be, and that there are, other cases, in which, although we cannot exhibit mechanism, or prove indeed that mechanism is employed, we want not sufficient evidence to conduct us to the fame conclusion.
There is what may be called the chymkal part of our frame; of which, by reason of the impersection of our chemistry, we can attain to no distinct knowledge: I mean, not to a knowledge, either in degree or kind, similar to that which we possess of the mechanical part of our frame. It does not therefore afford the fame species of argument as that which mechanism affords; and yet it may afford an argument in a high degree satis*. factory. The gastric juice, or the liquor which, digests the food in the stomachs of animals, i» of this class. Of all menstrua it is the most active, the most universal. In the human
stomach, stomach, for instance, consider what a variety of strange substances, and how widely difserent from one another, it, in a few hours, reduces to one uniform pulp, milk, nr mucilage. It seizes upon every thing, it dissolves the texture of almost every thing, that comes in its way. The flesh of perhaps all animals; the seeds and fruits of the greatest number of plants; the roots and stalks and leaves of many, hard and tough as they are, yield to its powerful pervasion. The change wrought by it is different from any chymical solution which we can produce, or with which we are acquainted, in this respect as well as many others, that, in our chymistry, particular menstrua act only upon particular substances. Consider moreover that this-fluid, stronger in its operation than a caustic alkali or mineral acid, than red precipitate or aqua fortis itself, is nevertheless as mild, and bland, and inoffensive to the touch or taste, as faliva or gum water, which it much resembles. Consider, I say, these several properties of the digestive organ, and of the juice with which it is supplied, or rather with which it is made to supply itself, and you will confess it to be entitled to a name, which it has sometimes
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 impersection of our chymistry; for, should the time ever arrive, which is not perhaps to be despaired of, when we can compound ingredients, so as to form a solvent, which will act in the manner in which the gastric juice act?, we may be able to ascertain 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 acquiescing in the inference, which a production of nature, by its place, its properties, its action, its surprising efficacy, its invaluable use, authorizes us to draw in respect of a creative design?
Another most subtle and curious function of animal bodies is secretion. This function is semi-chymical and semi-mechanical; cal; exceedingly important and diversified in its effects, but obscure in its process and in vt apparatus. The importance of the secretory organs is but too well attested by the diseases, which an excessive, a deficient, or a vitiated secretion is almost sure of producing. A sin~ gle secretion being wrong, is enough to make life miserable, or sometimes to destroy it. Nor is the variety less than the importance. From one and the fame blood 1I speak of the human body) about twenty different fluids are separated; in their sensible properties, in taste, smell, colour, and consistency, the most unlike one another that is possible? thick, thin, fair, bitter, sweet: and, if from our own we pass to other species of animals, we find amongst their secretions not only the most various, but the most opposite properties; the most nutritious aliment, the deadliest poison; the sweetest perfumes, the most fetid odours. Of these 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 secreted, made use of in the animal economy ; are evidently subservient, and are actually contributing to the
utilities utilities of the animal itself. Other fluids seem to be separated only to be rejected. That this also is necessary (though why it was originally necessary, we cannot tell) is shewn by the consequence of the separation being long suspended; which consequence is disease and death. Akin to secretion, if not the same thing, is assimilation, 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 ship with its furniture is composed. We have no operation of art wherewith exactly to compare all this, for no other reason perhaps than that all operations of art are exceeded by it. No chymical election, no chymical analysis or resolution of a substance into its constituent parts, no mechanical sifting or division, that we are acquainted with, in persecution or variety come up to animal secretion. Nevertheless the apparatus and process are obscure; not to fay, absolutely concealed from our. enquiries. In aJ&w, and only a few instances, we can discern a Iktle-dr" the constitution of a gland. In the. Whiffs of large animals we can trace the ^hiulgent artery dividing itself into an infmttfc number