END OF FILTH THEORY OF DISEASE. 235 



From the middle until nearly the close of the nineteenth century, 

 the germ theory, during the period when it was little else than a 

 theory, furnished many arguments for those who contended that filth 

 was a fertile source of disease. Putrefaction and fermentation were 

 known to be similar processes, and were believed to be due to the vital 

 activity of minute organisms. There were good grounds for believ- 

 ing that diseases of an infectious nature were also dependent on the 

 growth in the body of similar 'germs,' and this theory from 1850 grew 

 rapidly into favor. The germ theory led Dr. Farr, Registrar General 

 of England, to classify most of the infectious diseases as 'zymotic' or 

 fermentative diseases, for the disease poison was supposed to act, as in 

 truth it does, as a ferment in the blood or other tissues in the body. If 

 both putrefaction and disease were due to the action of minute organ- 

 isms, what more reasonable than to believe, said the theorists, that 

 putrefying material harbored and developed the 'germs' of disease? 



The filth theory then, which has had such a powerful influence on 

 the public mind, assumed that most of the infectious diseases were 

 directly and specifically caused by germs or other more subtle emana- 

 tions from decaying animal or vegetable matter. 



Furthermore, it was claimed that while such emanations might 

 not in every case produce a specific disease, they did tend almost 

 always to affect injuriously the general health, and lower the vitality 

 of persons habitually exposed. Hence the sewer gas theory which has 

 found such acceptance, and which has taught that the gas formed from 

 the filth in drains is so injurious to human life that portions so minute 

 as not to be appreciated by the senses are yet harmful in the extreme. 

 It was taught by medical men and health officials that filth and decay 

 in every form were a serious menace to health, both from the disease 

 germs which they contain, and the poisonous gases which they give 

 off; and this teaching is received and accepted, even to-day, by a large 

 portion of the medical profession, health officers and the public at 

 large. 



It is true that ever since this theory was promulgated some have 

 been led to doubt its dicta, because in the first place they often found 

 filth to abound where little zymotic disease existed, and even where the 

 'general health' of the people was high. On the other hand, zymotic 

 diseases were frequently found in the cleanest of dwellings, and where 

 the best of plumbing kept out all sewer gas. But most sanitary officials 

 accepted the theory as fact, and acted accordingly, some used it simply 

 as a working theory awaiting more definite knowledge, and a few were 

 led by their experience to allow it little weight in their work. 



As soon as the germ theory of disease ceased to be a mere theory, 

 and the true facts in regard to the etiology of the infectious diseases 

 began to be known, and bacteriology gave us exact knowledge of the 



