The whole problem of controlling infections sounds simple, depending as it does for the most part upon unpolluted water, milk, and food, extermination of certain insects, and cleanliness in personal behaviour. In practice the problem is not so easy. Public sanitation has performed miracles in the past, and will do much in the future; behaviour, however, will continue to be influenced by many factors, social and economic as well as personal. Ignorance of the laws of health is an obstacle to progress, but in modern conditions even the instructed may be unable to control their ways of living and working. Indeed, such control is at present limited to the privileged few. On the ignorant and the poor, those least able to bear it, society loads the heaviest burden of sickness. Only when ignorance and poverty are
abolished, as one day they will be, can the final stage be reached in the fight for public health.
THE NON-COMMUNICABLE DISEASES
In this group is included a great variety of maladies. Of some the causes are known, while in the case of others, origin, prevention, and remedy are still obscure. Here belong defects in structure of the body, both hereditary and acquired; insanity and other nervous diseases; new growths, like tumors and cancer; disturbances of bodily processes, as malnutrition and gout; and the important class of degenerative diseases, like arteriosclerosis, in which tissues become hardened and fibrous and hence less able to perform their normal functions.
The degenerative diseases are playing a menacing part in national health. The average length of life in the United States has shown a marked increase it is true, during the last 40 years. But this gain represents chiefly the saving of life through prevention of communicable diseases, especially among babies and children; among people who have passed the 30th year on the other hand, death rates are actually increasing. This increase is most marked after the age of 45, and is caused chiefly by the increase of cancer, and of degenerative diseases of the heart, blood vessels, and
kidneys. Degeneration of tissues is normally a condition typical of old age, and in aged persons it may occur in any tissue. There is no elixir of youth, and for old age there is no cure. But the important facts in this connection are that degenerative changes now occur prematurely, and that among a vast number of people, in various classes of society and various occupations, the vital organs show a marked tendency to break down after the age of 45.
This condition is not inevitable. Before the beginning of the present war, death rates at all ages were decreasing in England, Sweden, and other European countries. In America also degenerative diseases can be checked or prevented to a large extent, and it is highly important that their causes should be generally understood.
The two groups following include some of the probable causes:
1. Conditions of life which result in continued overwork, and mental overwork in particular; worry, excitement, insufficient recreation and exercise, and other kinds of nervous strain typical of modern life, especially in cities.
2. Irritating substances in the body, including poisonous substances resulting from infectious diseases, and from syphilis in particular; poisons from chronic infections, alcohol, and industrial