tricts according to industry and standard of life, it became possible to make inductive studies of health and sickness. Matthew Carey found, in 1794, that yellow fever chose seven-eighths of its victims among the poorer and less cleanly sections then about market and the river. He saw that wealth and culture were not immune because of any inherent or acquired grace, but that heaven, helping those who helped themselves, spared those whose standards of life made it possible to fly from the city into suburbs, or, if within the city, made cleanliness and drives and exercise, prompt expert medical attendance and isolation, possible. These conclusions need no modification because of the recent theory that mosquitos brought that same yellow pest. Boards of health were from Carey's time appointed, not for the sake of those sections that were supposed to cause epidemics, but for the benefit of the merchants, lawyers, women of the world, etc., who suffered discomfort and loss and interruptions, the leading motive of each being economic rather than hygienic. It is significant that the first vital statistics of the time were published by an economist to prove the financial loss entailed by epidemics, and that a great merchant established the first fever hospital and introduced trained nurses. This same simple economic motive has written stringent rules for the control of smallpox, typhoid, diphtheria, scarlet fever, and even consumption in nearly all communities, however small. But because based upon the interest of the few, the motive is intermittent in its action and waits upon crass and dramatic stimuli, hence we are conscious of these health rules only when danger is near and epidemic imminent.
So long as sanitation meant protection for those who had the greatest share in the returns from production, actual rather than potential dangers were treated. No great structural changes were to be expected. Had this leisure-class motive persevered, unaided by the philanthropic and socialistic elements of the last two stages, sanitary science would have stopped at the level of Philadelphia's former lethargy with reference to typhoid. The filtration plant never would have been built by the classes that can afford to buy spring water, nor could it have been delayed
