It seems quite a long time since we have had a genuine debauch of hearty laughter in the theatre, of "Laughter holding both his sides." There has been a great deal of laughter, but it must be remembered that there are several kinds of laughter. So much difference exists between one species of laughter and another that the close observer can guess from the nature of the laughter in the theatre what is the sort of piece which provokes it.
No doubt the subject of laughter is one of great difficulty. On the point one may quote a passage from Darwin: "Many curious discussions have been written on the causes of laughter with grown-up persons. The subject is extremely complex ... laughter seems primarily to be the expression of mere joy or happiness. The laughter of the gods is described by Homer as 'the exuberance of their celestial joy after their daily banquet.'" This, perhaps, hardly agrees with the popular idea of the term "Homeric laughter."
It may be that in the phrases of Darwin one sees a key to the difference between the laughter at witty dialogue and the laughter caused by comic situation, the former being an expression of intellectual amusement, not necessarily accompanied by "mere joy or happiness," whilst the latter is to a great extent the outcome of simple, non-intellectual human pleasure. In the case of a witty comedy one hears ripples of laughter rather than waves, and they have no cumulative effect, one may even laugh during a great part of the evening without reaching that agony of laughter which comes from an intensely funny situation--in fact, each laugh at dialogue is to some extent independent of the others. In the case of a funny situation there is a crescendo, and sometimes each outburst of laughter begins at the highest point reached by the outburst before it, till an intense pitch is attained; and, in fact, there is really no complete subsidence at all till the top of the climax is arrived at, but one is chuckling in between every spasm.
The term "screamingly funny" has a real meaning; one reaches an almost screaming pitch that leads to something like physical exhaustion, and certainly causes an aching of the sides, and even tears.
Another quotation from Darwin: "During excessive laughter the whole body is often thrown backwards and shakes, or is almost convulsed; the respiration is much disturbed; the head and face become gorged with blood, with the veins distorted; and the orbicular muscles are spasmodically contracted in order to protect the eyes. Tears are freely shed." On this one may refer to a phrase by Sir Joshua Reynolds: "It is curious to observe, and it is certainly true, that the extremes of contrary passions are, with very little variation, expressed by the same action." Yet another passage from Darwin: "With Europeans hardly anything excites laughter so easily as mimicry, and it is rather curious to find the same fact with the savages of Australia, who constitute one of the most distinct races in the world."