LAUGHTER (AS. hlruhtor, from Jrrhhan, Icel. Oa ja.(;oth. hlethjan, 011(;. hlahhon, Ger. lachen, to laugh; probably imitative in origin). A form of expression (q.v.) of the pleasurable emotions. In the smile, which is probably genetically a feeble of the laugh, the eorners of the mouth are drawn up ward and backward, and the cheeks are raised, by the contraction of the great zygomatic the upper lip is slightly raised; the upper and lower eyelids are somewhat approxi mated by the contraction of the orbicular muscles; the eyes are brightened owing to their greater tenseness, which results from these mus cular contractions or the increased blood pressure within the eyeball. The 'graduation' of the smile into the laugh is eharaeterized by the enhancement and spread of the motor phe nomena ; the mouth is opened: there are deep inspirations, followed by short, spasmodic, ex piratory movement:, especial ly of t he dia phragm ; the vocal cords are contracted, giving the typical sound: of laughter. In violent. spas modic laughter, the respiratory disturbances arc increased; there are also circulatory changes (quickened pulse, congested face) ; glandular dis charges (secretion of tears) ; distortions of the whole lusly, usually by the bead back and curving the trunk backward; and involun tary and purposeless movenients of the limb:.
The cause: of laughter are not always easy Of assignment. It seems to he primarily the ex pression of mere joy or happiness (notably in the ease of ehildren), yet it may be incited Ify what seem to be purely physiological agencies, e.g. tickling, cold, hysteria, and even some kinds of acute pain. Fiirthermore, in the adult it is also provoked by 'the ludierous,' and, indeed, Its so far dependent upon this factor that sonic writers regard laughter as always and intrinsic ally a response to a ludicrous sitnation. Thus Hol rhos says that blighter is ''a sudden glory, arising from a sudden conception of some emi neney in ourselves by eoniparison with the in firmity of others or with our own formerly." This may satisfactorily answer Spencer's question— "What induces us to laugh on reading that the eo•pulent Gibbon was unable to rise from his knees after making O tender declaration %"—but it is hard to believe that, as some assert, we laugh at the infirmity' or degradation of man kind when we are told that the Chinese man darin who committed suicide by eating gobldeaf (lied of a eonseiousness of inward guilt. Still less
is this proposition suited to the explanation of that laughter which is merely the indication of extreme pleasure, or abundant `animal spirits.' To explain this, Herbert Spencer invokes the principle of `dynamogenesis'; he reduces the dis play of muscular excitement to physiological con ditions, in terms of the discharge of energy through the pathways of the nervous system. Laughter may he produced by strong feeling of almost any kind; its movements are purposeless, and thus symptomatic of uncontrolled nervous discharge. The overflow takes place along the easiest and most used routes, i.e. to the facial, articulatory, and respiratory muscles. The laugh ter at the ludicrous (which is always a 'descend ing incongruity,' a drop from great to small) is similarly due to the fact that "a large amount of nervous energy, instead of being allowed to expend itself in producing an equivalent amount of the new thoughts and emotions which were nascent, is suddenly checked in its flow. . The excess roust discharge itself in some other direction. and there results an efflux through the motor nerves to various muscles, producing the half-convulsive actions we term laughter." Dar win concludes that, hr adult laughter, the person inust be in a generally pleasant mood, and that usually something incongruous, unaccountable, exciting surprise, and some sense of superiority ninst be the cause. lle finds the conditions of laughter at the ludicrous strikingly analogous to those of laughter at tickling.
BIBLIOGRAPHY. Bell, The Anatomy and PhilosBibliography. Bell, The Anatomy and Philos- ophy of Expression as Connected with the Fine A its (7th ed., London. 1893) ; Darwin, The E.c pression of the Emotions in Ilan and Animals (New York. 1890) ; Mantegazza, Physiognomy and Expression, Contemporary Science Series (London, 1884 ) ; Spencer, "The Physiology of Laughter." in Essays: Scientific, Polities!, and Nperula tire (New York, 1804) ; Titeliener. Out line of Psychology (New York, 1899) t Hecker, Physiologic Psychologie des Lachens rued des Kornisehen (Berlin. 1873) ; Sully, An Essay on Lady) tee (New York, 1902),