Page:Observations on Man 1834.djvu/118

 The benumbed limb feels larger, because any gross body, which encompasses and presses upon a limb by its weight or stricture, deadens the vibrations in it; and therefore conversely, when the vibrations are so deadened from a different cause, the idea of a gross encompassing body, or, which is almost the same thing, of the enlargement of the limb, will be suggested to the mind. But this circumstance must be referred to the head of association.

When the benumbed part begins to recover its feeling, violent prickings are often perceived. Now these seem to take place in the points where the natural vibrations first return; suppose at the ends of the nervous papillæ, and to arise from the conflict between the natural vibrations in these points, and the languid ones in the neighbouring parts. However, they come to an equality at last, by their mutual influences, as well as by the return of the natural vibrations to all the parts; which may serve to shew how itching ceases at last of itself. Friction helps to disperse and remove these prickings, and to restore the lost sensibility, which is very suitable to the notion of vibrations, and to the effect which it has in itchings.

If the hand be held down, and shaken, its muscles being first relaxed by a voluntary power, a numbness will be occasioned, in which the fingers feel large, for the reason given above. This numbness seems to arise from the irregular agitations, or vibrations, excited in the small parts; which, being different from the natural ones, or those in which sensibility consists, must check them; just as the agitations of water from the wind hinder the free propagation of regular undulations from a stone cast into it; or as any commotion of the air checks the free and distinct communication of a sound. It seems also, that those irregular and dissonant vibrations, which shaking the hand causes in the small medullary particles of its nerves, may pass on from part to part, though not so freely as regular ones.

From hence we may proceed to consider the numbness occasioned by the stroke of the torpedo. For the oscillations of this fish’s back may neither be isochronous in themselves, nor suitable to those which existed previously in the hand; and yet they may be so strong as not only to check and overpower those in the part which touches the fish, but also to propagate themselves along the skin, and up the nerves, to the brachial ganglion, and even to the spinal marrow and brain; whence the person would first feel the stupefaction ascend along the arm to the shoulder, and then fall into a giddiness, and general confusion, as is affirmed to happen sometimes. Some effects of concussions of the brain, and perhaps of the spinal marrow, also of being tossed in a ship, of riding backwards in a coach, and of other violent and unusual agitations of the body, seem to bear a relation to the present subject. But it would be too minute to pursue these things.

When a palsy arises from an internal cause, we may suppose,