One further observation is worth making.  Among the several sets of channels into which surplus feeling might be discharged, was named the nervous system of the viscera.  The sudden overflow of an arrested mental excitement, which, as we have seen, results from a descending incongruity, must doubtless stimulate not only the muscular system, as we see it does, but also the internal organs; the heart and stomach must come in for a share of the discharge.  And thus there seems to be a good physiological basis for the popular notion that mirth-creating excitement facilitates digestion.

* * * * *

Though in doing so I go beyond the boundaries of the immediate topic, I may fitly point out that the method of inquiry here followed, is one which enables us to understand various phenomena besides those of laughter.  To show the importance of pursuing it, I will indicate the explanation it furnishes of another familiar class of facts.

All know how generally a large amount of emotion disturbs the action of the intellect, and interferes with the power of expression.  A speech delivered with great facility to tables and chairs, is by no means so easily delivered to an audience.  Every schoolboy can testify that his trepidation, when standing before a master, has often disabled him from repeating a lesson which he had duly learnt.  In explanation of this we commonly say that the attention is distracted—­that the proper train of ideas is broken by the intrusion of ideas that are irrelevant.  But the question is, in what manner does unusual emotion produce this effect; and we are here supplied with a tolerably obvious answer.  The repetition of a lesson, or set speech previously thought out, implies the flow of a very moderate amount of nervous excitement through a comparatively narrow channel.  The thing to be done is simply to call up in succession certain previously-arranged ideas—­a process in which no great amount of mental energy is expended.  Hence, when there is a large quantity of emotion, which must be discharged in some direction or other; and when, as usually happens, the restricted series of intellectual actions to be gone through, does not suffice to carry it off; there result discharges along other channels besides the one prescribed:  there are aroused various ideas foreign to the train of thought to be pursued; and these tend to exclude from consciousness those which should occupy it.

And now observe the meaning of those bodily actions spontaneously set up under these circumstances.  The school-boy saying his lesson commonly has his fingers actively engaged—­perhaps in twisting about a broken pen, or perhaps squeezing the angle of his jacket; and if told to keep his hands still, he soon again falls into the same or a similar trick.  Many anecdotes are current of public speakers having incurable automatic actions of this class:  barristers who perpetually wound and unwound pieces of tape;