In refutation of this idea there is one more dogma packed for transportation, which I should like to offer in the form of a logical fallacy which the mediæval logicians put down in Latin terms: "_Post hoc, ergo propter hoc_": "After this, therefore because of this." One of our duties as doctors and social workers is to combat fallacies, to teach people to think straight instead of crooked about their ill health and their other troubles. When thus occupied, a large part of our labors will consist in trying to overcome the popular fallacy quoted above. "You went into a particular industry and you had tuberculosis: therefore you had tuberculosis _because_ you went into that industry." "You had a given disease and you took a certain remedy: you got better, _therefore_ the remedy cured the disease." So the superstitions flourish. I do not believe it is easy for any of us to extricate ourselves from that particular fallacy, but we must try. In industrial disease we have the causative factor of industrial hardship intimately mixed up with other factors. One of my colleagues, Dr. Roger I. Lee, of whose book I have already spoken, investigated, in our clinic at the Massachusetts General Hospital, the cases of one hundred young working-girls, factory employees, who either had tuberculosis or were suspected of tuberculosis--were in what is wrongly called the "pre-tubercular stage," when the doctor has not made up his mind whether the patient has tuberculosis or not. He studied these cases, as people ought to study them, always in proper coöperation with a social worker. He made his own careful observations in the dispensary. Then he employed a social worker to study the girls in the home and outside the home, following up in their lives and personalities the tangles of disease. His total result was that he could not say in any given case that industry had produced a single one of the diseases which he found, though he was not willing to swear that it had not done so. He found that a certain number of these girls, in their perfectly natural search for recreation, were running around the streets or elsewhere until the small hours of the morning. That is an obvious factor in producing a diseased state. It is not that we want to blame people for seeking recreation; but the results cannot also serve as evidence of the harm done by industry, except in a very wide sense in which we might say that industry does harm because it does not provide for recreation, which is, I think, an extreme view.