Principles of general and comparative physiology : intended as an introduction to the study of human physiology ... / by William B. Carpenter.
- William Benjamin Carpenter
- Date:
- 1839
Licence: Public Domain Mark
Credit: Principles of general and comparative physiology : intended as an introduction to the study of human physiology ... / by William B. Carpenter. Source: Wellcome Collection.
488/528 page 454
![contractions being produced by a galvanic current transmitted along the motor nerves. It may be objected to this doctrine, however, that other stimuli besides galvanism are capable of occasioning muscular contraction when applied to the nerves; that no unequivocal manifestation of electri- city has ever been produced by nerves along which the motor influence is being powerfully transmitted (as evidenced by the muscular contractions it excites); and that many of the conditions of the operation of the two agents are so dissimilar that their identity seems scarcely admissible.*' The motor influence seems really to issue from the cerebro-spinal axis, which gives rise to all the motor nerves; but, when excited by the will, it probably originates in the cerebral hemispheres. It may, however, be produced quite independently of the will, and without any influence from the brain, in modes that will presently be explained (§ 590). 587. The complexity of the operations of the mind, and the impossi- bility of deriving, from the study of the lower animals, any assistance which can be relied upon in their analogies, have hitherto been a com- plete bar to the successful investigation of them as a portion of the func- tions of the nervous system. It is yet quite uncertain how far mental acts are dependent on or connected with any changes in its condition; and we only know that they can neither be excited in the first place, nor effect any change upon the material structure of the body, except through its intervention. All acts of thought are either immediately or remotely dependent upon sensations; and, if all their inlets were closed from the first, the mind avou]d remain dormant, like the seed buried deep in the earth. The activity of the mind is just as much the consequence of ex- ternal impressions by AA'hich its faculties are called into play, as is the life of the body the result of the excitement of its several vital properties by external stimuli; and just as many animals are capable of retaining a certain degree not only of vitality but of vital action, Avhen deprived for a time of these stimuli, (as in hybernation), so could the mind which had once been roused retain its poA\rers by the recall of its former sensations, though debarred from the excitement of neAv ones. 588. The acts of mind in which the intellectual faculties are con- cerned can only produce an influence on the corporeal structure, by an exertion of the will, which, being propagated from the brain to the cerebro-spinal axis, excites in it a motor impulse that is propagated to the muscles. But various mental operations are independent of the employ- ment of the intellect, and can produce an influence on the motor nerves by some channel distinct from the will. Of this kind are the emotional actions, which, though aroused by sensations, are independent of the will, and often strongly opposed to it. It is only AA’hen the emotions are strongly excited, hoiArever, that the actions performed in obedience to them have this character; if less vehement, or partially subdued by the * See Alison’s Physiology, p. 117.](https://iiif.wellcomecollection.org/image/b28708532_0488.jp2/full/800%2C/0/default.jpg)
