in buildings, is proved by a microscopic examination of deposits from furniture, which shows a large percentage of animal refuse, mostly horse offal, ground up by the street traffic. 'Dirt is useful matter in a wrong place,' was one of the lamented Colonel Waring's maxims. He had, indeed, not only succeeded in removing it, but was in a fair way to make it pay for the cost of removal. Sanitation and economy often go hand in hand.
Concerted action is necessary to suppress this nuisance. No one should complain about dust who is not doing his share in preventing it. Each citizen must be his own sanitary officer and each sanitary officer and employee must be made to attend to his duties on public property. Corporations operating public conveyances should also be strictly held up to their duties. A case which illustrates this point is the New York Subway. Dust from the streets, mixed with sputum and sweepings from within, are permitted to accumulate indefinitely on a roadbed of gravel, which can never be thoroughly cleaned. The trains continually stir up some of this accumulation and impart it to the air. This is an inexcusable offense from a hygienic point of view. We need only consider that an underground route has not, like a surface railway, the natural assistance of wind, rain and sun in maintaining salubrity, and that it requires extra care and attention to make up for such disadvantage. The drippings of oil will not altogether bind or lay the dust, and the present method of drawing in air through dirty sidewalk gratings can not improve matters in this respect. An easily cleaned surface and effective mechanical means should be provided to keep the road-bed and the entire tunnel 'clean as a hound's tooth.' The stuffy atmosphere often noticed in the subway is largely traceable to these impurities, which are more objectionable than the heat and the exhaustion of the air. The latter, after all, may be regarded as temporary drawbacks, while dust and bacteria inhaled during the shortest transit will cause infection, threatening disease to any one predisposed. Unless built and operated with a reasonable appreciation of hygienic science, subways may at times become a serious menace to public health, especially when grip and similar epidemics are prevailing.
Causes for Impure Air in Buildings.—Among the numerous factors which may contribute to vitiate the air in buildings, some can always be eliminated, while others are unavoidable and should be counteracted by ventilation, in one form or another. Acting on the principle that prevention is better than cure, we should pay attention first to the avoidable sources. Waste matter of any kind is certain to contaminate the air without necessarily being perceptible by odor or by any of the customary methods of testing. Dust and dried-up sputum from the street, brought in by the air or by clothing, unless frequently removed, will permeate carpets and draperies, from where it is continually