With regard to laughing, there is, of course, another element that must be remembered. A hearty laugh moves the diaphragm up and down vigorously, empties and ventilates the lungs, stimulates the heart mechanically by its action upon the intra-thoracic viscera, and is one of the best tonics that we have for the circulation in the abdominal cavity, and probably also for the important nervous mechanisms centered there. Its action upon the lungs is readily recognized. Its influence upon the heart is usually not so much thought of, but deserves even a more prominent place. It is now well known that when patients have gone into coma or the apneic condition that sometimes follows shock, or the administration of an anesthetic, when the heart ceases to beat, the only effectual means of resuscitation is by directly irritating the organ. It has been suggested that if the abdominal cavity is open the surgeon's hands should be passed up and should squeeze the heart through the diaphragm. It has even been proclaimed that tapping on the chest vigorously over the precordium may arouse a heart that has for the moment stopped beating. It is easy to understand, then, that a hearty laugh, by stirring up all the intra-thoracic viscera, stimulates the heart mechanically and sets it beating more vigorously than before. This is one of the reasons why people feel so well after a hearty laugh. Even slight swallows of water act as a distinct heart stimulant. When people have fainted, a succession of swallows of water, each of them acting as a heart tonic, is one of the best methods that we have of stimulating the heart's action. It is usually said that this action is a consequence of the reflex from the terminal filaments of the vagus nerve running back and reflected down again to the heart. To me it has always seemed that the swallowing action had a direct mechanical effect upon the heart, because the esophagus passes so close to it in the thoracic cavity. Man is the only animal that laughs, and, as the old philosophers point out, he might very well be defined as _animal risibile_ with just as much truth as by the words _animal rationale_. It requires reason in order to have a sense of humor. The higher the reason, the more the humor. Peasants and the uneducated have, as a rule, a very undeveloped sense of humor. It is the highly educated man of deep intellectual powers who catches all the humor of a situation, and, though his expression of it may not be loud, it is deep and helpful at moments of depression. Humor is, of course, very different from wit, which is biting and which seems almost to be shared by the animals, if we can judge from the fact that they appear, occasionally, to play practical jokes upon one another.