Page:Popular Science Monthly Volume 17.djvu/848

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HE theory that contagious diseases as well as putrefaction and fermentation are developed and propagated by the agency of organisms allied to the bacteria has been widely accepted, and is supported by the results of recent investigations. It becomes, then, of paramount importance to ascertain the most efficacious means of destroying these organisms.

With this object in view, these researches into the conditions under which bacteria may be destroyed have taken three directions: 1. To test an observation made by Ernst Baumann, that the putrefactive organisms in the course of their action develop carbolic acid, a deadly poison to them, and to inquire whether there are not other poisons to bacteria developed in a similar manner; 2. Investigations prosecuted during the prevalence of the plague to ascertain whether a dry disinfection of clothing and goods could be made effective wholly to destroy the infectious organisms; 3. Having transplanted active infectious organisms from one substance to another to which they are suited, to arrest them in the most rapid stage of their development, destroy them, or cause them to perish.

In order to make the experiments of real value, a sure means must be found of knowing whether the organisms are alive or dead; they may seem dead when they are only passive. The only unfailing test is afforded by the reproductive faculty: when reproduction ceases, and can not be excited, the organisms may be considered dead.

Particular investigators have doubted whether it is possible wholly to destroy these lower organisms. Naegeli says it can not be fully done without the aid of heat, and even heat is not always equally effective. They are generally more easily destroyed by heat when moist than when dry, but even a boiling heat will not destroy some of them when they are in fluids of a neutral reaction. The more acid the reaction, the less is the degree of heat that is required. The degree of heat required to destroy the germs of infectious diseases is believed to be greater than it is practicable to apply by the dry process to clothing and similar materials. The capacity of many of the organisms to reproduce may, indeed, be destroyed by a more moderate temperature, but a question remains concerning the germs or spores which had been taken up into the materials and were carried away with them. These are believed to have some kind of a coating which enables them to resist what destroys the parent organisms.

In order to test the value of the dry process as applied to infected