any distinct ideas: they simply feel pleasure, and express it by
laughter or smiles. With imbeciles rather higher in the scale, personal
vanity seems to be the commonest cause of laughter, and next to this,
pleasure arising from the approbation of their conduct.
With grown-up persons laughter is excited by causes considerably
different from those which suffice during childhood; but this remark
hardly applies to smiling. Laughter in this respect is analogous with
weeping, which with adults is almost confined to mental distress,
whilst with children it is excited by bodily pain or any suffering, as
well as by fear or rage. Many curious discussions have been written on
the causes of laughter with grown-up persons. The subject is extremely
complex. Something incongruous or unaccountable, exciting surprise and
some sense of superiority in the laugher, who must be in a happy frame
of mind, seems to be the commonest cause.[804] The circumstances must
not be of a momentous nature: no poor man would laugh or smile on
suddenly hearing that a large fortune had been bequeathed to him. If
the mind is strongly excited by pleasurable feelings, and any little
unexpected event or thought occurs, then, as Mr. Herbert Spencer
remarks,[805] a large amount of nervous energy, instead of being
allowed to expend itself in producing an equivalent amount of the new
thoughts and emotion which were nascent, is suddenly checked in its
flow. ... The excess must discharge itself in some other direction,
and there results an efflux through the motor nerves to various classes
of the muscles, producing the half-convulsive actions we term
laughter. An observation, bearing on this point, was made by a
correspondent during the recent siege of Paris, namely, that the German
soldiers, after strong excitement from exposure to extreme danger, were
particularly apt to burst out into loud laughter at the smallest joke.
So again when young children are just beginning to cry, an unexpected
event will sometimes suddenly turn their crying into laughter, which
apparently serves equally well to expend their superfluous nervous
energy.
The imagination is sometimes said to be tickled by a ludicrous idea;
and this so-called tickling of the mind is curiously analogous with
that of the body. Every one knows how immoderately children laugh, and
how their whole bodies are convulsed when they are tickled. The
anthropoid apes, as we have seen, likewise utter a reiterated sound,
corresponding with our laughter, when they are tickled, especially
131