Transformation, etc., of Pathogenic Microbes. 99 



upon spores, upon germs contained in a liquid or 

 moist medium than upon those which are in a dry- 

 medium. 



The time necessary for destruction by light varies 

 from a few hours to some weeks, according to the 

 case; solar light, however, is a sure agent and one 

 whose beneficial action operates in a continuous man- 

 ner; hence, we should guard against voluntarily de- 

 priving ourselves of it; abundance of light in inhab- 

 ited places is one of the most rational of hygienic 

 measures. 



Desiccation. — Insufiiciency of water arrests the mul- 

 tiplication of microbes ; the latter then lose their vi- 

 tality more or less rapidly. But the spores resist 

 much longer than the bacteria themselves ; we know, 

 indeed, that the virus of symptomatic charbon is 

 dried in order to preserve it, and that the germs of 

 tuberculosis are preserved active for a long time in 

 pulverulent sputum. 



Oxygen. — The germs of the air are destroyed more 

 or less quickly under the combined influence of des- 

 iccation, which arrests their pullulation and impairs 

 their vitality, of oxygen, which oxidizes them, and 

 of the solar light, which excites in them this oxida- 

 tion; the oxidizing action of oxygen, without doubt, 

 extends itself to the bacteria of waters and of the 

 soil, these perishing more or less rapidly by reason of 

 the conditions unfavorable to their multiplication 

 which they meet in these media. 



Other natural agents, less important, may intervene 

 to destroy pathogenic bacteria; among these we will 

 notice again the ordinary saprogenic germs which, 

 finding themselves in the same media as the patho- 



