Page:Popular Science Monthly Volume 21.djvu/193

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183
PSYCHOLOGICAL EXPERIMENTATION.

his investigations into the fifth and seventh nerves of the head, the present doctrine of the spinal nerves is nowhere explicitly stated. These memoirs can scarcely, indeed, be read in any other sense; and "A Manual of Anatomy," published by Mr. John Shaw (another brother-in-law) in 1821, contains a tolerably clear intimation of it. Moreover, Mr. J. Shaw, having visited Paris in 1821, and having repeated to Magendie the experiments on the fifth and seventh nerves which he had made with Sir C. Bell, further pointed out to him (as appears from Magendie's own narration)[1] the analogy of the fifth to the spinal nerves, and attributed to the double roots of these "regular" nerves this double function of motion and sensation.

It was at this point that Magendie took up the experimental inquiry, both as to the roots of the spinal nerves and the functions of the fifth and seventh nerves of the head; and it will be convenient to dispose of the latter in the first instance. He showed that the second of the three divisions of the fifth pair is a nerve of sensation only; so that the part of the face which it supplies (between the eyes and the upper lip) depends for its motor action on the seventh pair, which he regarded as the ordinary motor nerve of the face, ministering to its voluntary movements, as well as to those of expression and respiration. These corrections (which were confirmed by other experimenters) were not only accepted by Sir C. Bell, but were appropriated by him as his own; the reprints of the two memoirs just referred to being altered in successive editions of his "Nervous System of the Human Body," by omission, addition, and variation, not only without any acknowledgment of the source of the correction, but without the least intimation of a change. It is clear, therefore, that although he shrank from making experiments himself, he was ready enough to profit by those of others.

On testing experimentally Bell's idea of the functions of the anterior and posterior roots of the spinal nerves, and varying his experiments in every way he could think of, Magendie was only able to arrive at this general conclusion—that the anterior roots are more especially motor, and the posterior more especially sensory. For he could not get over the fact that irritation of the anterior roots in the living animal called forth signs of pain, and that irritation of the posterior roots called forth movements. The repetition of the same experiments by others gave no more conclusive results; until, in 1831, Johann Müller (afterward the celebrated Berlin professor) was able, by a very carefully devised method of experimentation upon frogs, to show that, for these animals at least, Bell's doctrine was correct. And it was by the extension of the same method to warm-blooded animals, and by the light of the new ideas then dawning[2] as to the "reflex

  1. "Journal de Physiologie," October, 1821.
  2. The very clear ideas long before promulgated by Prochaska on this point had been entirely forgotten.