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upon the fyftem of intermediate actions between the spring and the pointer. What thus ftruck his attention in the feveral parts of the watch he might probably defignate by one general name of "relation:" and obferving, with respect to all the cafes whatever, in which the o ign and form tion of a thing could be afcertained by evidence, that these relations were found in things produced by art and defign, and in no other things, he would rightly deem of them as characteristic of fuch productions. To apply the reasoning here described to the works of nature.

The animal œconomy is full; is made up of these relations.

I. There are firft, what, in one form or other, belong to all animals, the parts and powers which fucceffively act upon their food. Compare this action with the process of a manufactory. In man and quadrupeds, the aliment is, firft, broken and bruifed by mechanical inftruments of maftication, viz, fharp fpikes or hard knobs, preffing against, or rubbing upon, one another: thus ground and comminuted, it is carried by a pipe into the ftomach, where it waits to undergo a great chymical action, which we call digeftion:

when

when digested, it is delivered through an orifice, which opens and fhuts as there is occafion, into the first inteftine: there, after being mixed with certain proper ingredients, poured through a hole in the fide of the veffel, it is further diffolved: in this ftate, the milk, chyle, or part which is wanted, and which is fuited for animal nourishment, is ftrained off by the mouths of very fmall tubes, opening into the cavity of the inteftines: thus freed from its groffer parts, the percolated fluid is carried by a long, winding, but traceable courfe, into the main ftream of the old circulation; which conveys it, in its progress, to every part of the body. Now I fay again, compare this with the process of a manufactory; with the making of cyder, for example, the bruifing of the apples in the mill, the fqueezing of them when fo bruifed in the prefs, the fermentation in the vat, the beftowing of the liquor thus fermented in the hogsheads, the drawing off into bottles, the pouring out for ufe into the glafs. Let any one fhew me any difference between thefe two cafes, as to the point of contrivance. That which is at prefent under our confideration, the "relation"

of

The

of the parts fucceffively employed, is not more clear in the last case, than in the firft. aptnefs of the jaws and teeth to prepare the food for the ftomach, is, at least, as manifeft, as that of the cyder-mill to crush the apples for the prefs. The concoction of the food in the ftomach is as neceflary for its future use, as the fermentation of the ftum in the vat is to the perfection of the liquor. The difpofal of the aliment afterwards; the action and change which it undergoes; the route which it is made to take, in order that, and until thats it arrive at its deftination, is more complex indeed and intricate, but, in the midst of complication and intricacy, as evident and certain, as is the apparatus of cocks, pipes, tunnels, for transferring the cyder from one veffel to another; of barrels and bottles for preferving it till fit for use, or of cups and glaffes for bringing it, when wanted, to the lip of the confumer. The character of the machinery is in both cafes this, that one part answers to part, and every part to the final

another

result.

This parallel between the alimentary opera tion and fome of the proceffes of art, might be

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carried

carried further into detail. Spallanzani has remarked * a circumftantial resemblance between the ftomachs of gallinaceous fowls and the ftructure of corn-mills. Whilft the two fides of the gizzard perform the office of the mill-ftones, the craw or crop fupplies the place of the hopper. When our fowls are abundantly supplied with meat they foon fill their craw; but it does not immediately pafs thence into the gizzard. It always enters in very fmall quantities, in proportion to the progrefs of trituration: in like manner as in a mill a receiver is fixed above the two large ftones which ferve for grinding the corn; which receiver, although the corn be put into it by bushels, allows the grain to dribble only in small quantities into the central hole in the upper mill-stone.

But we have not done with the alimentary hiftory. There fubfifts a general relation between the external organs of an animal by which it procures its food, and the internal powers by which it digefts it. Birds of prey, by their talons and beaks, are qualified to feize and devour many fpecies, both of other

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birds, and of quadrupeds. The conftitution of the ftomach agrees exactly with the form of the members. The gaftric juice of a bird of prey, of an owl, a falcon, or a kite, acts upon the animal fibre alone; will not act upon feeds or graffes at all. On the other hand, the conformation of the mouth of the sheep or the ox is fuited for browfing upon herbage. Nothing about thefe animals is fitted for the pursuit of living prey. Accordingly it has been found by experiments, tried not many years ago with perforated balls, that the gastric juice of ruminating animals, such as the sheep and the ox, speedily diffolves vegetables, but makes no impreffion upon animal bodies. This accordancy is ftill more particular. The gaftric juice even of graminivorous birds, will not act upon the grain, whilft whole and entire. In performing the experiment of digeftion with the gastric juice in vessels, the grain must be crushed and bruised, before it be fubmitted to the menftruum, that is to fay, must undergo by art, without the body, the preparatory action which the gizzard exerts upon it within the body, or no digeftion will take place. So ftrict is the relation between the offices affigned to the digeftive or

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