LAUGHTER, n. An interior convulsion, producing a distortion of the
features and accompanied by inarticulate noises. It is infectious
and, though intermittent, incurable. Liability to attacks of laughter
is one of the characteristics distinguishing man from the animals --
these being not only inaccessible to the provocation of his example,
but impregnable to the microbes having original jurisdiction in
bestowal of the disease. Whether laughter could be imparted to
animals by inoculation from the human patient is a question that has
not been answered by experimentation. Dr. Meir Witchell holds that
the infection character of laughter is due to the instantaneous
fermentation of _sputa_ diffused in a spray. From this peculiarity he
names the disorder _Convulsio spargens_.
-- Ambrose Bierce, "The Devil's Dictionary"
