238 POPULAR SCIENCE MONTHLY. 



that this disease is carried in fomites, t. 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 grati- 

 tude to Surgeon Eeed 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 out- 

 side 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 harm- 

 less. 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 



