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.
It seems almost absurd that a physician should tell patients that it will do them good to practice smiling, to take every possible opportunity to laugh, and even to take frequent glances into a looking glass, to see that they are not pulling long faces. The difference between a feeling of melancholy and one of gladness consists mainly in the position of the outer angles of the mouth. The putting into practice of the maxim, not to let the sad lines dominate the countenance, but to insist on keeping the others there as far as possible, means much for the correction of internal feelings of depression and discouragement that may be badly interfering with the flow of nerve impulses from the brain to the body.
Mouth Breathing.—Since Meyer's discovery of the overgrowth of the lymphoid tissue in the pharynx, we have learned to appreciate how important is mouth breathing, even for the intellectual life. We all knew before, and indeed from time immemorial it was well understood, that, as a rule, people who went around with their mouths open were of low grade intelligence. All sorts of methods were used to teach these young people to keep their mouths shut. They were reminded of it at home, they were told about it at school, and, if they married, their wives tried to keep them from this apparent manifestation of lack of intelligence. Of course, they were not, as a rule, able to carry out the well-meant intentions of their friends and advisors. The mouths were kept open because they could not breathe normally through their noses, and so respiration had to be accomplished by the only other available avenue. As a consequence of the open mouth, the lips were inclined to roll out somewhat, and certain indications of the human physiognomy were supposed to be associated with these thick lips.
Now we know the real meaning of the condition. Mouth breathing is possible, but it is inadequate. Insufficient respiration leads to insufficient oxidation of tissues, and to lowered vitality in all structures, and this is particularly notable in the brain, as well as in certain other higher structures. It is not because the individuals are lacking in intelligence that their mouths are open, but because the same reason that compels the open mouth also affects their intellectual activity. The blocking of nasal respiration lowers vital activity of all kinds. Hence the lowered intellectual vitality. The thick lips, which are supposed to be characteristic of a certain passionateness of nature, and which usually are associated with a lack of thorough control over animal inclinations, probably owe their significance to the fact that this special peculiarity of feature usually accompanies mouth breathing, and that the individual who labors under this deficient respiration, is likely to lack control to at least some degree. There is even a question whether the deficient oxidation is not likely to be much more notable in its effect upon the higher faculties than on the lower, and as a consequence the latter develop somewhat to the detriment of the former.
These studies in physiognomy may, indeed, be correlated in many ways with distinct physical conditions instead of as formerly with the general constitution of the individual. For instance, large protruding eyes used to be said to be characteristic of nervous, timid, sensitive individuals, easily scared, and not well able to take up the harder parts of the battle of life. Now we know that this feature is usually associated with an excess of secretion of the thyroid gland, and that the nervousness is not a matter of character so much as it is due to the disturbance of internal metabolism consequent upon this interference with the proper function of an important organ. It might well be called a slight thyroid intoxication. In large amounts it produces all the symptoms of Graves' disease.
Bodily Conditions and Stupidity.—We have many illustrations of the influence of the body on the mind, when purely physical causes work rather serious results on disposition and character and energy. A typical example was the so-called tropical anemia which existed in Porto Rico when the Americans took possession of the island. There were so many cases of it that out of about 25,000 deaths reported in 1903, nearly 6,000 were from so-called anemia. Investigation of the conditions soon revealed the real cause. It had been thought to be due to a combination of the climate, malaria and the lack of nutrition on the part of the country people. The people were absolutely without ambition, they had no energy, they seemed scarcely able to keep body and soul together, and they cared for nothing except to get just enough to supply them with a meager sustenance. Of incentive to lift themselves up, there was none. This was largely attributed by the first Americans who went to the island to the conditions which had existed under Spanish rule, as the Spaniards had not encouraged manufactures or industries in the island, and had left the people without any incentives to the awakening of enterprise or initiative.
Hook-Worm Disease .—Before long it was found that the real reason for the anemia of the Porto Ricans was the presence in their intestines in large numbers of the so-called hook-worm. These worms exhausted the vitality of the sufferers and left them without surplus energy and, indeed, with scarcely enough life to care whether or not life itself continued. It was not a moral condition, but a very definite physical cause that was at work. Shortly afterwards it was found that the same disease existed in our Southern states among the so-called "poor whites." Before this, these people had been supposed to be a characterless, unambitious, lazy people, who cared not to get on, who had sunk to about the lowest depths possible for civilized people, and who were quite satisfied to remain there. The discovery of hook-worm disease among them, however, soon made it clear that their laziness was the result of the drain upon their systems due to the presence of thousands of hook-worms. When these were removed, if nature was not already exhausted, the "poor whites" became normal human beings once more with ambition and initiative.
This story of pathology influencing racial qualities is not new in the history of the world. It is not improbable that even certain periods of decadence in Egyptian history which have ordinarily been attributed to the so-called running out of particular ruling races or families, or to the degeneration of the people consequent upon luxury, were really the result of the spread of the hook-worm disease through certain portions of Egypt. Dr. Sandwith, who has studied the disease very carefully in Egypt, is sure that it has existed there for at least four thousand years, and that the descriptions of certain affections which occurred in Egypt in historic times were really due to the same cause as now is known to produce the so-called Egyptian chlorosis, the name that was used for hook-worm disease in Egypt. Workers in soil, and in mines and in tunnels, are especially likely to be affected by it, and whenever it is neglected it spreads rather widely, as is seen in the mines of Germany and Hungary at the present time. As the cause was unrecognized in the olden time, it is possible that periods of supposed lassitude among the people were really due to infection by this parasite.
Malaria and Degeneration .—In recent years it has come to be generally recognized that the decadence of Greece, for instance, was not due to moral causes so much, perhaps, as to physical reasons. During the classic periods in Greece there are no traces of malaria. After the invasion of Sicily, the expedition against Syracuse and other attempts on the part of the cities of Greece to spread their dominion, malaria seems to have been introduced among her people, and as the anopheles mosquito was already there, the malaria spread widely, and in the course of a century affected so many of the people that their energy and ambition and initiative were to a great extent destroyed. It is well known that these effects often occur as a consequence of malaria, and as generation after generation is affected by the disease, are emphasized more and more. The relaxing effect of tropical climates, of which we have heard so much, and which is supposed after a time to bring about the inevitable production of a race eminently lazy and careless of the future, is probably