it most clearly and familiarly; the infectiousness of laughter is notorious and as irresistible as the infection of fear itself....  The great laugher is the person of delicately responsive sympathetic reactions; and his laughter quickly gives place to pity and comforting support, if our misfortune waxes more severe.  Such persons are in little danger of giving offense by their laughter; for we detect their ready sympathy and easily laugh with them; they teach us to be humorous.

H. Merian Allen in his essay “Little Laughs in History” says “The relaxation of a full laugh clears the brain, restores fit contact with one’s fellows, and so smoothes the way for the solving of knotty problems.”

Linus W. Kline, Ph.D., further elucidates the psychical office of humor as follows: 

The psychical function of humor is to delicately cut the surface tension of consciousness and disarrange its structure that it may begin again from a new and strengthened base.  It permits our mental forces to reform under cover, as it were, while the battle is still on.  Then, too, it clarifies the field and reveals the strategetic points, or, to change the figure, it pulls off the mask and exposes the real man.  No stimulus, perhaps more mercifully and effectually breaks the surface tension of consciousness, thereby conditioning the mind for a stronger forward movement, than that of humor.  It is the one universal dispensary for human kind:  a medicine for the poor, a tonic for the rich, a recreation for the fatigued and a beneficient check to the strenuous.  It acts as a shield to the reformer, as an entering wedge to the recluse and as a decoy for barter and trade.

Humor is as necessary to our mental and spiritual life as are vitamins to our physical well-being.  Ruskin has called our attention to the tendency of rivers to lean a little to one side, to have “One shingly shore upon which they can be shallow and foolish and childlike, and another steep shore under which they can pause and purify themselves and get their strength of waves fully together for due occasions,” and has likened them to great men who must have one side of their life for work and another for play.  Action and reaction must be balanced:  seriousness and lightness.  “Men who work prodigously must play with equal energy,” says one commentator.  “Humor is the gift of the deeply serious man,” remarks another.  “There have been very few solemn men, but their solemnity was evidence, not of their gifts, but of their defects; as a rule greatness is accompanied by the overflow of the fountain of life in play.”  “The richly furnished mind overflows with vitality and deals with ideas and life freely, daringly, often audaciously.”

The function of the catalyst in chemical reactions is to help other bodies to get on together, but in doing this it only lends its presence.

    Catalyst. A chemical body which by its presence, is capable
    of inducing chemical changes in other bodies while itself
    remaining unchanged.