Tuberculosis is not considered an industrial disease, although in certain dusty trades involving the inhalation of particles of silica there may be a relationship between pulmonary tuberculosis and occupation. Despite the non-occupational character of pulmonary tuberculosis in general, the peculiar conditions of modern industry have tended to expose workers to more massive and repetitive concentrations of tubercle bacilli than other segments of the population. Unfavorable social and economic factors such as crowding, at home and in the workshops, and low income are clearly reflected in the tuberculosis mortality data. Every study of urban housing has shown that tuberculosis death rates in the crowded areas of cities are many times greater than the rates in the less crowded areas; and that industrial workers and their families are concentrated in these areas. The death rate of tuberculosis (all forms) for males is higher among residents of large cities than among residents of cities of intermediate size. The rate in smaller cities in turn is much higher than that in rural areas. Dublin, in an analysis of Metropolitan Life Insurance records, finds that between the ages of 35 and 44, death rates from pulmonary tuberculosis in industrial male policyholders is about 2% times that of non-industrial policyholders. Propagation of the tubercle bacillus finds a fertile soil in cities, where many people live and work in close quarters and even breathe each day a certain number of cubic feet of air shared with other persons. It may well be that the dosage of bacilli plays an important role in the production of clinical tuberculosis; on this basis alone one may expect to find greater opportunities of infection among the people in densely populated areas. Industrial buildings such as the Ford Bomber Plant at Willow Run and office buildings such as the Pentagon in Washington, are good examples of modern industry's tendency to concentrate ever larger groups of human beings in limited spaces in the pursuit of wage earning. It should also be remembered that approximately one-third of the average adult's life is spent in the task of earning a living. A lower standard of living appears to be intimately associated with lowered resistance—the second factor in the production of tuberculosis. In a study of tuberculosis mortality among industrial workers by Rollo H. Britten, it was found that the rate among unskilled workers, ages 25 to 44, was four times as high as among professional, business, and clerical workers of the same age group. High concentrations of tubercle bacilli in the environment and low-