pleasure or pain; each of which is felt in the region of the diaphragm.

Lively genius, and brilliant imagination, are often too apt to lose their way in their journeying through philosophy. At first, supported by a few leading facts, they feel bold, and push on, as on the sure road. A cross turn meets them, they then are obliged to alter their course, and eventually perhaps have nothing but conjecture and hypothesis to guide them the rest of their way. But, though there should be contradictory phænomena, I would not dissuade the inquisitive mind from such curious, if not advantageous excursions; particularly, as there is no branch of inquiry which is secure from illusion, or exempt from controversy. Whether the brain be the radix, and the diaphragm be the plexus of the nerves; or whether the one be the soil, and the other be the seat only of the ve getable ramifications; I confess myself incapable of determining. One thing, however, is certain, that the stomach sympathizes with every part of an animal, and that every part sympathizes with the stomach; therefore, whatever acts upon the stomach, and rouses its natural and healthy actions; and whatever affects it, so as to produce debility, has an immediate effect upon

This sympathy is

every part of the body. strongest in the vital parts. Besides this universal sympathy between the stomach and all the parts of the body, there are peculiar sympathies for instance, the heart immediately sympathizes with the lungs. If any thing be received into the lungs, which is a poison to animal life, such as inflammable air, or volatile vitriolic acid, the motion of the heart immediately ceases; and from experiment it appears, that any thing salutary to life, applied to the lungs, will restore the action of the heart, after it has been at rest for a considerable time. * And thus, whatever the absolute causes of sensation may be, one thing seems clear, that motion inevitably appertains to it, in all its forms; whether, for example, we hear music, or taste savours, or smell odours, or feel a stone, or see light.

* John Hunter,

+ Harris.

• LET

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LETTER LII.

IN the formation and arrangement of the parts of animal bodies, a wonderful and inconceivably various mechanism is observable. But, in such soft and yielding materials, the motive power must be incomprehensibly great, both as to the continuation of the many different motions, constantly going on in the several parts of the body, as the heart, stomach, lungs, intestines; and to the renovation of those motions that are interrupted, and restored by turns, as walking, working, or speaking. In the action. of soft bodies upon soft bodies, it has often been demonstrated, that the motion is always diminished. How much then, and how constantly must it be diminished, in the yielding softness of the flesh and fluids of animal bodies? Let us reflect how soon water settles, after motion impressed, by the bare attrition of its parts on one another, although it has no obstacles to encounter, or narrow passages to move through. Motion is easily continued or communicated in free spaces, especially if the moving body be hard

and

and firm: but, it is quite otherwise in the veins, arteries, intestines, and lacteal vessels of the bodies of animals; in the narrow twining meanders, which convey the fluids constantly to innumerable parts. The capacity of these slender tubes could not admit the finest hair; and the mazes and windings are to us inexplicably perplexed and intricate. What a quantity of attrition must there be, while the blood, lymph, · and chyle creep through these, not even microscopic vessels! No mathematician, yet, hath been able to calculate the attrition of the parts of fluids upon one another, while they move against the sides of such narrow channels, or for their loss of motion, in the constant change of their direction. The power, that urges the fluids in animal bodies ten thousand different ways at once, has never yet had a term of art assigned it by philosophers. It acts upwards, against the nature of gravity. Attraction be→ tween the particles of fluids does not help us out. Attraction to all sides would rather stop motion, as it does between the particles of liquors. The alternate contraction and dilatation of the coats of the vessels, is a postulate, which supposes the thing to be explained mechanically; and it is no where applicable but to the heart and to the arteries. It is an attempt as full of blindness

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blindnes as of vanity, to offer to account me chanically for the circulation in the animal body. In the womb, we are not only fearfully and wonderfully formed, but we are, every minute after, fearfully and wonderfully preserved. Thus, says a celebrated anatomist, we who attend to dissections, are little better acquainted with the true state of the human frame, than the porters and errand boys are with the politics of the city they inhabit. Like them, we know every street, every alley, every passage; but like them too, we are ignorant of what is going forward in the mansions, to which these passages lead. But, is this mechanism the work of matter and motion? The motion is constantly consumed, and new force is constantly impressed.*

It has been calculated, that when a man extends his arm, and, upon the extremity of his fore fingers, supports as great a weight as he can in that posture, the force that is exerted in the muscles to support this weight, is more than seventy thousand times greater than the weight. itself. What a lever, and what a fulcrum! But, we cannot trace the inexpressible subtilty of this mechanism. Neither are we, a fortiori, pre

posterously

* Baxter.

† Borelli.