Sympathetic laughter does not arise from any contemplation of ludicrous circumstances, but is only a sort of reflection of the feelings of others.  There seems to be little intelligence in it, but something almost physical, just as yawning is infectious, or as on seeing a person wounded in a limb we instinctively shrink ourselves in the same part of the body.  Even a picture of a man laughing will have some effect upon us, and so have those songs in which exuberant mirth is imitated.  Thus we often laugh without feeling just cause, as we often feel cause without laughing.  All exhibitions of emotion are infectious.  We feel sad at seeing a man in grief, although the source of his sorrow is unknown to us; and we are inclined to be joyous when surrounded by the votaries of mirth.  Not unfrequently we find a number of persons laughing, when the greater part of them have no idea what is the cause of the merriment.  Sometimes we cannot entirely resist the impulse, even when we ourselves are the object of it, so much are we inclined to enter into the feelings and views of those who surround us.  In this, as well as in many other cases, the sight and proximity of others exercise over us a great influence, and sometimes almost a fascination.

To this sympathy we are largely indebted for the diffusion of high spirits.  It is pleasant to laugh and see others laughing, and thus the one leads to the other.  “Laugh and be fat,” is a proverb, and it has been well observed that “we like those who make us laugh,” because they give us pleasure.  We may add that we like to see others joyous, because we feel that we are surrounded by kindly natures.  A gallant writer tells us that he hopes to be rewarded for his labours in the field of literature by “the sweetest of all sounds in nature—­the laughter of fair women.”  Macready, speaking of this influence, says: 

“The words of Milman would have applied well to Mrs. Jordan, ’Oh, the words laughed on her lips!’ Mrs. Nesbitt, the charming actress of a late day, had a fascinating power in the sweetly-ringing notes of her hearty mirth; but Mrs. Jordan’s laugh was so rich, so apparently irrepressible, so deliciously self-enjoying, as to be at all times irresistible.”

The agreeable influence of smiles is so well known that many are tempted to counterfeit them, and assume an expression in which the eye and lip are in unhappy conflict.[3] On the other hand, painful thoughts are inimical to mirth.  No sally of humour will brighten the countenance of a man who has lately suffered a severe loss, and even mental reflection will extinguish every sparkle.  But the bed of sickness can often be better cheered by some gay efflorescence, some happy turn of thought, than by expressions of condolence.  Galen says that AEsculapius wrote comic songs to promote circulation in his patients; and Hippocrates tells us that “a physician should have a certain ready humour, for austerity is repulsive both to well and ill.”  The late Sir Charles Clark recognised this so far that one of his patients told me that his visits were like a bottle of Champagne; and Sir John Byles observes, “Cheerfulness eminently conduces to health both of body and mind; it is one of the great physicians of nature.