Page:Observations on Man 1834.djvu/146

 villous coat. It cannot depend on associated circumstances in its common state, because, being perpetual, it is equally associated with every thing, i.e. particularly so with nothing. However, as grateful aliments increase it, the sight of them may do the same by association. Could we see our stomachs and bowels, it is probable, that we should get some degree of voluntary power over them.

Vomiting is sometimes, and a nausea often, excited by associated circumstances; and there have been instances of persons who could vomit at pleasure by first introducing some of these. But, I suppose, this action never follows the mere command of the will, without the intervention of some strong associated circumstance. We have, in like manner, a semi-voluntary power of restraining vomiting, for a time at least, by means of ideas of decency, shame, fear, &c.

Some persons have a power of expelling flatulencies from the stomach in a manner which is almost voluntary; and many imitate an automatic hiccough very exactly. It facilitates these powers, that both the motions here considered are very frequent especially during childhood. Those who can hiccough voluntarily, attain to it by repeated trials, as in other cases of voluntary actions.

The spasms, and violent motions of the bowels, cannot be expected to become voluntary. They do, however, seem to return in many cases, from less and less bodily causes perpetually, on account of associated circumstances, as has been already remarked.

In like manner, the vibrations which run up the excretory ducts of the glands, must be supposed to remain totally under the influence of their original causes; unless we except the contraction of the gall-duct, which happens sometimes in violent fits of anger. This may perhaps arise from vibrations excited by associated circumstances.

Both the power of expelling the fæces and urine, and that of checking this expulsion, are under the influence of many associated circumstances, and voluntary to a considerable degree. And it will easily appear, from the principles of this theory, that they ought to be so. The filling the chest with air by the contraction of the muscles of inspiration, is a circumstance which never attends these actions in their purely automatic state. Young children learn it by the same steps as they do other methods of exerting the greatest force, and to the greatest advantage. See Prop. XXII. Cor. I.

It deserves notice here, that the action of the muscular coat of the stomach and intestines is far less subject to the power of the will, than that of the great fleshy muscles of the trunk and limbs. The efficient cause of this is the great and immediate dependence which the action of the muscular coat has upon the sensations of the villous, on account of the exquisiteness of these