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POPULAR SCIENCE MONTHLY.

that this disease is carried in fomites, i. e., lives outside of the body, and is thus implanted in new localities, where it develops in a filthy soil, giving rise to new foci of the disease. We have been taught that by keeping a city thoroughly clean, yellow fever could be excluded as it would find no place to grow. Such methods, however, never have been and never could be successful. We all owe a great debt of gratitude to Surgeon Reed and his associates for teaching us the true method of combating this disease and dealing a death blow to the filth theory. By their experiments in which they failed to transmit the disease by fomites, they showed that the poison, the exact nature of which still remains unknown, does not live outside of the body and therefore can not develop in filth. The mosquitoes which transmit this disease do, unlike the malarial mosquitoes, often breed in filthy water, such aa cesspools, dirty gutters and the like, and this doubtless is the kernel of truth in the filth theory of its origin.

Thus one by one the zymotic diseases have been shown to be purely contagious, and not to have their origin in filth. In not a single one of these diseases has our more exact knowledge placed its source outside of man or other animals. But it may be argued that though the specific diseases may not arise from filth, we still have to fear the gaseous products of decomposition, and that the foul emanations from sewers, vaults and dung-heaps may undermine the health and pave the way for these diseases. Probably more sins have been attributed to sewer gas than anything else of this kind, but we now know that the air of modern sewers and well constructed drains is practically harmless. It is true that in confined cesspools and choked drains, injurious gases like sulphuretted hydrogen, marsh gas or carbon dioxide may be formed in such quantities as to be fatal to life, but in ordinary sewers and drains, with their facilities for ventilation and rapid motion of contents, such accumulations are impossible, and a slight leakage of sewer air, which was formerly considered so dangerous, has been shown by the chemists and bacteriologists to be harmless. Foul odors from manure piles, garbage barrels, soap works or offensive manufactories are when concentrated intensely annoying and often nauseating to those who only occasionally breathe them, but those who are constantly exposed to them do not suffer at all and do not notice them. It is also observed that plumbers and sewer cleaners are not at all affected by the odors to which they are exposed. When these odors are slight there is no reason to think that they affect the health at all, and in any event the disturbance which they cause is not lasting. The burden of proof lies with those who claim that the gases of decomposition are a serious menace to health. Most of the alleged proof relates to the production of specific diseases like typhus, typhoid and cholera which we now know can not be caused in any such way. Evidence tried by modern