2 36 POPULAR SCIENCE MONTHLY. 



life history of the minute organisms which are their cause, the erro- 

 neous generalizations of the filth theory became apparent. We can 

 now to a large extent discriminate between filth that is dangerous and 

 that which is not. We know that the gaseous emanations from decaying 

 matter do not produce specific disease. We know that the germs 

 themselves are much more rarely air borne than had been thought, 

 and that they are not thrown off into the air from the moist surfaces 

 of the materials where they are largely found. 



Observations of cholera outbreaks, both in England and this coun- 

 tiy, furnished the best arguments for the filth theory. This disease 

 was in a great number of instances traced to wells or streams polluted 

 with leakage from privies or drains. The disease abounded in filthy 

 locations and among filthy people. It was perhaps natural, though not 

 logical, to accuse all filth as likely to produce cholera. We now know 

 that cholera is due to the comma spirillum and that this germ is thrown 

 off from the patient in the discharges from the bowels, but that 

 outside the body it rarely survives a few days, and practically never 

 increases in number. Excrement from cholera patients may infect 

 drinking water and so cause the disease, or among the uncleanly, fecal 

 matter may be pretty directly transferred from one to another, or food 

 may become infected by hands soiled by fecal matter, or the germs may 

 be carried to the food by flies or other insects. 



It is not filth that causes cholera, but a particular kind of filth, 

 namely the excrement of cholera patients. Furthermore this filth and 

 its germs are not air borne, they are not breathed in, but taken in 

 through the mouth. This exact knowledge does away with the vague 

 fear of all filth as a cause of the disease, and greatly simplifies the means 

 necessarv to control it. It is true that the filth theorists did much to 

 prevent cholera, for in their warfare against filth they demanded a 

 water supply from a source which could not be contaminated, and they 

 demanded sewers to remove all excremental matter. These great 

 public improvements make it far easier to control cholera than it was 

 before their inception. The filth theorists were successful thus far, 

 because, so far as cholera was concerned, there was a modicum of truth 

 in their theory. 



What has been said of cholera is applicable also to typhoid fever. 

 This disease is due to a bacillus which does not grow outside of the 

 body, but is carried in excremental filth just as is the cholera spirillum, 

 and it must be controlled in just the same way. 



The diphtheria bacillus is also strictly parasitic and grows, except 

 in rare instances, on the mucous membrane of human beings. From 

 persons so infected it is transmitted to others, usually by means of cups, 

 spoons, pencils or other articles, or directly by kissing or fondling. 

 Diphtheria was a few years ago considered a filth disease and was 



