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Relations. WHEN several different parts contribute to one effect; or, which is the same thing, when an effect is produced by the joint action of different instruments; the fitness of such parts or instruments to one another, for the purpose of producing, by their united action, the effect, is what I call relation : and wherever this is observed in the works of nature or of man, it appears to me to carry along with it decisive evidence of understanding, intention, art. In examining, for instance, the several parts of a watch, the spring, the barrel, the chain, the fusee, the balance, the wheels of various sizes, forms, and positions, what is it which would take an observer's attention, as most plainly evincing a construction, directed by thought, deliberation, and contrivance? It is the suitableness of these parts to one another ; first, in the succession and order in which they act; and secondly, with a view to the effect finally produced. Thus referring the spring to the wheels, our observer sees in it, that which originates and upholds their motion ; in the chain, that which transmits the motion to the fusee; in the fusee, that which communicates it to the wheels; in the conical figure of the fusee, if he refer to the spring, he sees that which corrects the inequality of its force. Referring the wheels to one another, he notices, first, their teeth, which would have been with out use or meaning, if there had been only one wheel, or if the wheels had had no connexion between them. selves, or common bearing upon some joint effect; secondly, the correspondency of their position, so that the teeth of one wheel catch into the teeth of another ; thirdly, the proportion observed in the number of teeth of each wheel, which determines the rate of going. Referring the balance to the rest of the works, he saw, when he came to understand its action, that which rendered their motions equable. Lastly, in looking upon the index and face of the watch, he saw the use and conclusion of the mechanism, viz. marking the succession of minutes and hours ; but all depending upon the
motions within, all upon the system of intermediate actions between the spring and the pointer. What thus struck his attention in the several parts of the watch, he might probably designate by one general name of “ relation;" and observing with respect to all cases whatever, in which the origin and formation of a thing could be ascertained by evidence, that these relations were found in things produced by art and design, and in no other things, he would rightly deem of them as characteristic of such productions. To apply the reasoning here described to the works of nature.
The animal economy is full, is made up, of these relations:
I. There are, first, what, in one form or other, belong to all animals, the parts and powers which successively act upon their food. Compare this action with the process of a manufactory. In men and quadrupeds, the aliment is, first, broken and bruised by mechanical instruments of mastication, viz. sharp spikes or hard knobs, pressing against or rubbing upon one another: thus ground and comminuted, it is carried by a pipe into the stomach, where it waits to undergo a great chymical action, which we call digestion : when digested, it is delivered through an orifice, which opens and shuts as there is occasion, into the first intestine: there, after being mixed with certain proper ingredients, poured through a hole in the side of the vessel, it is farther dissolved : in this state, the milk, chyle, or part which is wanted, and which is suited for animal nourishment, is strained off by the mouths of very small tubes, opening into the cavity of the intestines: thus freed from its grosser parts, the percolated fluid is carried by a long, winding, but traceable course, into the main stream of the old circula. tion; which conveys it, in its progress, to every part of the body. Now I say again, compare this with the process of a manufactory; with the making of cider, for example; with the bruising of the apples in the mill, the squeezing of them when so bruised in the press, the fermentation in the vat, the bestowing of the liquor thus fermented in the hogsheads, the drawing off into bottles, the pouring out for use into the glass. Let any one shew me any difference between these two cases, as to the point of contrivance. That which is at present under our consideration, the “ relation" of the parts successively employed, is not more clear in the last case than in the first. The aptness of the jaws and teeth to prepare the food for the stomach, is, at least, as manifest as that of the cider-mill to crush the apples for the press. The concoction of the food in the stomach is as necessary for its future use, as the fermentation of the stum in the vat is to the perfection of the liquor. The disposal of the aliment afterward; the action and change which it undergoes; the route which it is made to take, in order that, and until that, it arrive at its destination, 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 cider from one vessel to another; of barrels and bottles for preserving it till fit for use; or of cups and glasses for bringing it, when wanted, to the lip of the consumer. The character of the machinery is in both cases this; that one part answers to another part, and every part to the final result.
This parallel between the alimentary operation and some of the processes of art, might be carried farther into detail. Spallanzani has remarked* a circumstan. tial resemblance between the stomachs of gallinaceous fowls and the structure of corn-mills. Whilst the two sides of the gizzard perform the office of the millstones, the craw or crop supplies the place of the hopper.
When our fowls are abundantly supplied with meat, they soon fill their craw: but it does not immediately pass thence into the gizzard; it always enters in very small quantities, in proportion to the progress of trituration; in like manner as, in a mill, a receiver is fixed above the two large stones which serve 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 millstone.
But we have not done with the alimentary history. There subsists
relation between the external
* Dis. 1. sect. liv.
organs of an animal by which it procures its food, and the internal powers by which it digests it. Birds of prey, by their talons and beaks, are qualified to seize and devour many species, both of other birds, and of quadrupeds. The constitution of the stomach agrees exactly with the form of the members. The gastric juice of a bird of prey, of an owl, a falcon, or a kite, aets upon the animal fibre alone; it will not act upon seeds or grasses at all. On the other hand, the conformation of the mouth of the sheep or the ox is suited for browsing upon herbage. Nothing about these 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 dissolves vegetables, but makes no impression upon animal bodies. This accordancy is still more particular. The gastric juice, even of granivorous birds, will not act upon the grain, whilst whole and entire. In performing the experiment of digestion with the gastric juice in vessels, the grain must be crushed and bruised, before it be submitted to the menstruum,
that is to say, must undergo by art without the body, the preparatory action which the gizzard exerts upon it within the body; or no digestion will take place. So strict, in this case, is the relation between the offices assigned to the digestive organ, between the mechanical operátion and the chymical process.
II. The relation of the kidneys to the bladder, and of the ureters to both, i. e. of the secreting organ to the vessel receiving the secreted liquor, and the pipe laid from one to the other for the purpose of conveying it from one to the other, is as manifest as it is amongst the different vessels employed in a distillery, or in the communications between them. The animal structure, in this case, being simple, and the parts easily separated, it forms an instance of correlation which may be presented by dissection to every eye, or which, indeed, without dissection, is capable of being apprehended by every understanding. This correlation of instruments to one another fixes intention somewhere.
Especially when every other solution is negatived
by the conformation. If the bladder had been merely an expansion of the ureter, produced by retention of the fluid, there ought to have been a bladder for each ureter. One receptacle, fed by two pipes, issuing from different sides of the body, yet from both conveying the same fluid, is not to be accounted for by any such supposition as this.
III. Relation of parts to one another accompanies us throughout the whole animal economy. Can any relation be more simple, yet more convincing, than this, that the eyes are so placed as to look in the direction in which the legs move and the hands work? It might have happened very differently, if it had been left to chance. There were, at least, three quarters of the compass out of four to have erred in. Any considerable alteration in the position of the eye, or the figure of the joints, would have disturbed the line, and destroyed the alliance between the sense and the limbs.
IV. But relation perhaps is never so striking as when it subsists, not between different parts of the same thing, but between different things. The relation between a lock and a key is more obvious, than it is between different parts of the lock. A bow was designed for an arrow, and an arrow for a bow: and the design is more evident for their being separate implements.
Nor do the works of the Deity want this clearest species of relation. The sexes are manifestly made for each other. They form the grand relation of ani. mated nature; universal, organic, mechanical : subsisting like the clearest relations of art, in different individuals ; unequivocal, inexplicable without design.
So much so, that, were every other proof of contrivance in nature dubious or obscure, this alone would be sufficient. The example is complete. Nothing is wanting to the argument. I sue no way whatever of getting over it.
V. The teats of animals which give suck, bear a relation to the mouth of the suckling progeny ; particularly to the lips and tongue. Here also, as before, is a correspondency of parts; which parts subsist in different individuals,