muscular reaction which is peculiarly well fitted to bring the needed relief? More special conditions may favour the movements of laughter in certain cases. As I have observed above, Darwin suggests that the rapid alternation of crying and laughing which occur among hysterical patients may be favoured by “the close similarity of the spasmodic movements”.[49] In other words, the motor centres engaged, when in the full swing of one mode of action, may readily pass to the other and partially similar action. This would help to account for the short outbursts of laughter during a prolonged state of painful agitation, and to explain the fact noted by Descartes, that no cause so readily disposes us to laughter as a feeling of sadness.[50] Our theory plainly requires that these sudden breakdowns or relaxations of strained mental attitudes should, even when only momentary interruptions, be accompanied by an agreeable sense of relief. I believe that those whose experience best qualifies them to judge will say that this is so. The dead weight of the fear, the poignancy of the grief, and the constraining effect of the situation of _gêne_, seem to yield at the moment when the “awful laugh” is snatched at. This comforting sense of a lightened load, though in part the direct result of a cessation of cerebral strain, would, as we have seen, pretty certainly derive added volume from the returning sense-reports telling of the ameliorated condition of the bodily organs. 3. We have considered two of the varieties of laughter {71} which lie outside the region of our everyday mirth. We may now pass into this region, and inquire, first of all, into the causes of those varieties which come under the head of joyous laughter. Here we shall best begin by touching on the simple and early form which may be called the overflow of good spirits. Darwin, as has been mentioned, rightly regards the full reaction of the laugh as the universal expression by our species of good spirits, of a joyous state of mind. We have now to examine the mode of production of this simple type. It is important to note that all experiences of pleasure do not bring on laughter. There are quiet enjoyments of a soothing character which are far from generating the powerful impulse needed for the movements of diaphragm and rib. To lie on a summer day in a hammock in a wood and indulge in the sweets of _dolce far niente_ is to be out of reach of the tickling imp. States of enjoyment, too, which, though exciting, require a measure of close attention, such as those occasioned by a glorious sunset, or stirring music, do not start the spasmodic contractions of muscle.