CHAPTER I.-INTRODUCTORY. PUBLIC HEALTH AND PREVENTABLE DISEASE. PUBLIC HYGIENE may be defined as that branch of sanitary science which concerns the physical condition of communities. It embraces a consideration, of the various influences operating upon society, whether for its material good or its actual deterioration, with the view of extending the former, and preventing, or ameliorating, as far as possible, the effects of the latter. It involves the enactment of laws by which the safety of the whole may be protected against the errors of a part, and, above all, it aims at the prevention of disease by the removal of its avoidable causes. In a wide sense, therefore, the science of public hygiene enlists the services of the people themselves in continuous efforts at self-improvement; of the teachers of the people, to inculcate the best rules of life and action; of physicians, in preventing as well as curing disease; and of lawgivers, to legalise and enforce measures of health-preservation. But while it is the special province of the medical profession, as guardians of the public health, to study the causes of physical deterioration and disease, and to point out how far these causes may be controlled or averted, the general well-being of the people must mainly depend on their own exertions and self-restraint. B Sanitary improvements in man's material surroundings will not compensate for social transgressions against laws of morality; for public virtue is essential to public health, and both to national prosperity. The time, however, has gone by when people can be dragooned into cleanliness or be made virtuous by police regulations, and hence it is that the most thoughtful among practical reformers of the present day base their hopes of sanitary progress on the education of the masses as the real groundwork of national health. The people must be taught that good conduct, personal cleanliness, and the avoidance of all excesses, are the first principles of health-preservation; that mental and physical training must go hand in hand in the rearing and guidance of youth; and that morality does not consist so much in a blind observance of the formulæ of empty creeds as in a hearty submission to precepts of health. Nor is this all. They must be interested systematically in the general results of sanitary progress, and become more intimately acquainted with the social and material causes by which it is impeded. Unless a knowledge of these fundamental principles of hygiene be widely disseminated amongst them, it is in vain to expect that legislative enactments, however well devised, will succeed in raising the standard of public health to any considerable extent. If it be objected that such knowledge cannot be imparted in schools, it may at all events be conveyed through the public press and from the pulpit; or is it too much to hope that the wordy warfare concerning the origin of human life may speedily give place to united efforts in striving to prevent its appalling waste? Taking, then, this wide view of the scope of public hygiene, the subject of public health and preventable disease may be briefly discussed under the following sections: : I. Hereditary Influence. II. Causes of Deterioration and Disease. SECTION I. HEREDITARY INFLUENCE. In Although there are many biologists who do not accept the Darwinian theory of "Pangenesis" in its entirety, there are few amongst them who dispute the influence of heredity which it serves so fully to explain. As regards the individual, the term heredity is the expression of the fact that a man is wholly built up of his own and ancestral peculiarities, and so far as these are concerned, it matters little or nothing what were the characteristics of the early progenitors of his race. other words, the accumulation of individual variations through recent descent has a far greater influence upon a man's bodily and mental constitution than the unchanged gifts of a remote ancestry, so much so, indeed, that these latter may be regarded as a vanishing quantity. This result of the Darwinian theory has been conclusively demonstrated by Mr. Galton in his work on Hereditary Genius, and it is especially valuable as affording a clear and succinct conception of the influence of heredity in all cases in which individual variations lie well within the limits of stability of a race. According to this view, the progeny is invariably moulded by the characteristics of its more recent ances |