Let us note, in conclusion, the scientific trend of the present day. A large proportion of medical work is of scientific interest rather than of direct utility for the patient. A concrete example will explain our meaning. A severe shivering, a sudden elevation of the temperature, a dulness on one side of the chest, the presence in the same position of crepitant râles, a rusty, sticky expectoration--such is the syndrome by which a practitioner recognises an attack of acute pneumonia. He knows its duration; he knows the relief which will be produced by the application of poultices. To ideas such as these may be reduced all that is indispensable for the doctor to know in order to exercise his art. The post-mortem examination of the hepatised lung, its increase in density, the histological study of the engorged air cells and bronchioles, the researches upon the pneumococcus, its culture, its vitality--all this constitutes a search into etiology and pathogenesis, whose aim is quite different. The same distinction may be made in the medical study of defective children. And from this point of view the results which at first seem of secondary importance reappear in the foreground. This is the case, for example, with the stigmata of degeneration. It would be unreasonable to attribute to them an individual value, and to utilise them for arranging children serially in the order of their mental deficiency; but in the work of synthesis they are decidedly significant, since their study leads one to consider them either as the effects of, and therefore as witnesses to, alterations in the nervous system, or as the consequences of causes sufficiently powerful to have modified that system. One would not deny all practical bearing to such investigations of pathogenesis. It is a mistake of Tolstoy to regard them as the pastime of refined dilettantes. When the biological study of defectives leads to this idea, that the mental weakness of the defectives, like the peculiarities in the character of the ill-balanced, is the result of degeneration--the result, for instance, of the alcoholisation of a people--it will quickly result in measures of social hygiene.