Licence: Public Domain Mark
Credit: The senses and the intellect / by Alexander Bain. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
109/679 (page 77)
![: same tiling : and what one centre does in a low degree . another may do in a higher ; the peculiar mode of operation ] is established as a fact of the nervous mechanism. (2.) The permanent closure of certain of the muscles— 1 those named sphincters—is an effect of the same nature as 1 the tonicity, hut displaying a more energetic stimulus still—a : stimulus that we can refer only to the spontaneous influence I of some one of the centres, hlo impression from without can be quoted as originating this contraction. Neither could the closure be ascribed to the muscle’s own contractility, which, as before remarked, may be allowed to count as something, seeing that the destruction, or paralysis, of certain of the centres leads to the total relaxation of those muscles. (3.) It is not altogether irrelevant, to cite the activity maintained by involuntary muscles, as showing the existence of a mode of power originating with the nerve centres. Nervous influence is required for maintaining the breathing action, the circulation of the blood, the movement of the food along the alimentary canal, &c.; but this nervoiis action must evidently flow from the eentres of its own accord. Even granting that _when once commenced, the impression arising from one move- ment is sufficient to stimulate the one that succeeds, which may be the case to some extent, as when the completed move- ment of expiration of the lungs initiates the succeeding in- spiration, the difiiculty would still present itself. How did the action commence at first ? By what influence do we draw our first breath,* or set on the first stroke of the heart ? If these activities cannot be kept up without the foreign assistance of nerve centres, they could not be commenced without such assistance, and so the nervous influence must precede, since we cannot suppose that a collapsed organ can originate the central stimulus that first sets it agoing.-f* * The power that commences respiration in the new-horn infant is still undecided. I do not wish to foreclose this question, or to deny that external stimulants may come into play to produce the effect. ■f Some physiologists would ascribe the tonicity, not to the exclusive influence of the centres, but to the existence of a constant stimulation pro-](https://iiif.wellcomecollection.org/image/b2491762x_0109.jp2/full/800%2C/0/default.jpg)
