We saw in the preceding chapter that during quite recent years the dangers of early life have been greatly lessened because of our increased knowledge of infantile hygiene, and from the fact that the infective diseases, which are always most dangerous to the young, have been greatly abated. We saw, however, at the same time, that the constitutional weaknesses of humanity are by no means lessened, and that there are strong grounds for believing that during the last thirty years the race has observably degenerated, a result to be anticipated from the withdrawal of selective influences during childhood and early life. Amongst these constitutional weaknesses we may specially notice defects in the respiratory, circulatory, nervous and other systems, as being of interest and importance, and their observation worthy of our close attention. In this little treatise it is impossible however to do more than shortly to allude to hereditary defects in the nervous system associated with incapacity, a tendency to insanity, or to excesses in the use of alcohol. The subject is not only one of popular interest, but it can be understood by those who are not technically instructed. Just as no two men agree in the possession of equally sound mucous membranes or lung tissues, so we may have decided variations in the brain tissues. Together with unsound brain tissue we have symptoms which we call mental derangement, and of these we have an infinite variety, starting from the mentally too excitable, or too inert, and passing on to those who are more obviously diseased and useless, and finally to those who are dangerous to society at large. Now, these brain affections are markedly hereditary--proverbially so indeed. It is true that an overplus of work, or anxiety, or depressing surroundings, may produce insanity or other nervous conditions in one who under better surroundings would undoubtedly escape. These are, no doubt, true exciting factors, but they act with alarming ease in the case of certain types, while in others their action is relatively inoperative. This type, an organic variation, is transmitted, it is not destroyed. As Dr. Bastian says: “It is now a well-established fact that persons who are endowed with a neurotic habit of body very frequently transmit a similar tendency to their children. It is not a tendency to any particular nervous disease, but a vulnerability of the nervous system as a whole, which is transmitted, so that under the influence of even a comparatively slight strain the weakness may manifest itself in one or other of several ways.” Speaking of the suicidal tendency, Dr. Maudsley remarks: “It is, indeed, striking and startling to observe how strong the suicidal bent is apt to be in those who have inherited it, and how seemingly trivial a cause will stir it into action. Persons affected by it will sometimes put an end to themselves on the occasion of a petty contrariety, or when they are a little out