in youth. But it is not performed voluntarily with the same force, as when from a pressing uneasiness in the lungs.
Coughing arises from an uneasy sensation in the wind-pipe fixing in the point of the epiglottis, as the sensation which causes sneezing does in the tip of the nose. This ought also to become voluntary, and to be weaker when voluntary, than when excited by a strong irritation.
Hawking is a voluntary action, derived from coughing, as blowing the nose is from sneezing. Spitting is nearly related to these actions. It tallies perfectly with the foregoing theory, that children cannot hawk, spit, or blow the nose, for some years.
Laughter is a nascent cry, recurring again and again, as has been observed before, Prop. XXVI. By degrees it puts on a certain type, and recurs again and again according to that type, just as other actions. And it is excited in young children not only by the sensation of tickling, which lies, as it were, between pleasure and pain, but by the apprehension of this, or any other apprehension sufficiently moderate, by every surprise, and every mental emotion that lies between pleasure and pain, and by all the associates of these, as particularly by seeing others laugh. And thus children laugh more and more, and get a power of performing the action of laughter at pleasure, though with less force than when it is excited by its proper cause in full vigour.
It is remarkable, that young brute creatures, in their sportings with each other, make such noises, as bear the same analogy to their violent cries, which laughter in us bears to crying from pain.
Bodily pain is attended with violent and irregular respiration on account of the violent and irregular vibrations, which, in this case, first ascend to the brain, and then descend into the diaphragm. Hence mental pain, which is the offspring of bodily pain, is attended also with violent and irregular respiration, i.e. with sobbing. The crying which used to attend bodily pain in childhood is often checked in the mental pains of adults by fear, shame, &c. i.e. by a voluntary or semi-voluntary power; and this seems to make the respiration so much the more irregular.
It is more difficult to account for the shedding tears from grief; for very young children are not apt to shed tears when they cry. It seems to me, that so great and general a disorder in the brain, as that which takes place in violent grief, must affect the fifth pair of nerves in a particular manner, so as to influence the lachrymal glands both directly, and also indirectly, viz. by the strong convulsions produced in the muscles of the eyes and face. The membranes of the fauces and nose are likewise affected in grief, as is evident from the sensations in the fauces, and tip of the nose; and thus vibrations may run to the lachrymal glands through the ductus ad nasum, and lachrymal points, as observed before in irritations from sternutatories, &c. Young children may not shed tears freely, because very great and general
