The first question which now presents itself is what is laughter? and our answer must be that it is a change of countenance accompanied by a spasmodic intermittent sound—­a modification of the voice—­but that we cannot trace its physical origin farther than to attribute it to some effect produced upon the sympathetic nerve, or rather the system of nerves termed respiratory.  These communicate with every organ affected in mirth, but the ultimate connection between mind and body is hidden from our view.

In all laughter there is more or less pleasure, except in that of hysteria, when by a sudden shock the course of Nature is reversed, and excessive grief will produce the signs of joy, as extravagant delight will sometimes exhibit those of sorrow.  We should also exclude the laughter caused by inhalation of gas, and that of maniacs, which arising from some strange and unaccountable feeling is abnormal and imperfect, and known by a hollow sound peculiar to itself.  None of these kinds of laughter are primary, they are but imperfect reflections of our usual modes of expression, and, excepting such cases, we may agree that M. Paffe is correct in observing that “Joy is an indispensable condition of laughter.”  Dr. Darwin refers to the laughter of idiots to prove that it may be occasioned by pleasure alone.  Strangely enough, he quotes as an instance in point the fact of an idiot boy having laughed at receiving a black eye.

Proceeding onwards, we next come to inquire why the sense of humour is expressed by voice and countenance, and does not merely afford a silent and secret delight?  The answer may be given, that one object, at least, is to increase social communication and multiply pleasure.  The well-being of the animal world largely depends upon the power of each member of it to communicate with others of the same species.  They all do so by sound and gesture, probably to a larger extent than we generally imagine.  A celebrated physician lately observed to me that “all animals have some language.”  How far mere signs deserve so high a name may be questioned.  But man has great powers of intercourse, and it is much owing to his superior faculties in this respect that he holds his place so high above the rest of creation.  Orators, who make it their study to be impressive, give full importance to every kind of expression, and say that a man should be able to make his meaning understood, even when his voice is inaudible.  It has been lately discovered that the mere movement of the lips alone, without sound, is sufficient to convey information.[2] Facial expression has been given us as a means of assisting communication, and smiles and laughter have become the distinctive manifestations of humour.  Thus the electric spark passes from one to another, and the flashing eye and wreathed lip lights up the world.  Profit also accrues—­fear of being laughed at leads us to avoid numerous small errors, and by laughing at others we are enabled to detect shortcomings in ourselves.