life history of the minute organisms which are their cause, the erroneous 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 country, 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