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Page:Popular Science Monthly Volume 21.djvu/191

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I then touched the anterior division; immediately the parts were convulsed."

"Experiment II.—I now destroyed the posterior part of the spinal marrow by the point of a needle; no convulsive movement followed. I injured the anterior part, and the animal was convulsed."

The experiments thus narrated by Bell in a letter to his brother, dated March 2, 1810, have been cited as proving that he had thus early attributed motor functions to the anterior roots, and sensory to the posterior. But the inference which he himself drew from them at the time was altogether different:

"It is almost superfluous to say that the part of the spinal marrow having sensibility [i. e., the anterior column] comes from the cerebrum; the posterior and insensible port belongs to the cerebellum."

Thus, although on the track of a great physiological discovery, Bell allowed himself to be completely diverted from it by his anatomical preconception. Of the true functional relations of the two sets of nerve-roots, there is not the remotest hint in this "Idea."

None the less, however, do I recognize in it what (to my mind) constitutes the real basis of Bell's claim to the elucidation of the meaning of the double origin of the spinal nerves. "Considering," he said, "that the spinal nerves have a double root, and being of opinion that the properties of the nerves are derived from their connections with the parts of the brain, I thought that I had an opportunity of putting my opinion to the test of experiment, and of proving at the same time that nerves of different endowments were in the same cord and held together by the same sheath." This was, unquestionably, one of the most fertile suggestions that the insight of a man of genius has ever put forth for the guidance of physiological inquiry; and, even if Bell had never himself pursued it further, he would clearly be entitled to a very large share of any discoveries that others might make by working upon it. It seems, however, as if the unsatisfactory character of the results he obtained and his dislike to experimentation upon living animals turned his thoughts in a different direction; and he applied himself for some years to the study of the nerves of the face, on the peculiarities of whose anatomical distribution he seems to have long pondered, with the idea that these might furnish him with the key of which he was in search.

Bell, as is well known, had considerable artistic ability; and one of the earliest of his publications was his very valuable "Anatomy of Expression," in which he pointed out how close is the relation between many of the muscular movements by which the emotions are expressed and those concerned in respiration. Still, as it would seem, under the "dominant idea" of a special set of nerves for the "vital and involuntary motions," he assigned this special motor function to the seventh pair, which arises by a single root, and supplies the muscles of the face generally; while he supposed the fifth pair, which arises (like