Industrial disease is a phrase we have heard much in the last ten or fifteen years, meaning that diseases are caused--some of them--by the conditions to which people are exposed in industry. A great deal of indignation, some of it fruitful, much of it harmful, has been aroused against employers and against the whole system of industry--because we have now recognized the fact of industrial disease. Employers in the past have been more interested in their machinery than in their human help. That is not only bad, but very stupid. Most of us believe that because it is stupid it is not likely to continue indefinitely. But aside from all these matters of controversy, there is one important distinction to make at the start. (_a_) Industrial disease in the narrow, strict sense, i.e., something produced by the industry, something which would never have occurred in any form if the person had not been in that industry. (_b_) Disease affected, modified, in some way by industry, but due in part to other causes. There are very few clear-cut and common industrial diseases. Lead poisoning is almost the only one. Disease due to the inhalation or swallowing of other poisons and the penetration through the skin or irritation of the skin by definite poisons are real dangers, but not common. More common, more difficult to deal with, and therefore more within the province of the social worker, are the diseases in which industry is only one factor in the complicated skein of causes. Take such matters as exposure to unusual heat or cold, unusual humidity or dryness in industry--very common conditions; or still more, exposure to unusual strain and hurry from what we call "speeding-up" or from the piece-work system. I do not think there is any good evidence that those things produce any single disease. I think there is excellent evidence that they often dip the scale whereby a person who has been in equilibrium, able to get along with his outside troubles, and to keep his balance, is finally knocked down into disease. A person has tuberculosis. One of the favorite tricks of unscrupulous political orators is to say, "Look at all that tuberculosis due to the greed and the cruelty of employers!" Bad conditions of industry are doubtless a factor in the production of tuberculosis, but we must realize how many and important the other factors are. The eight or ten hours a person spends in industry is often a small factor in producing his ill health, compared to the fourteen or sixteen hours he spends outside the industry. Hence if we are to understand the diseases of workmen we must investigate _these_ hours just as carefully as those in the factory. That is what we ordinarily omit. We find so many cases of tuberculosis in a given industry, and we say, "Ah, then, these cases are _due_ to the hardships of that industry."