DISINFECTION 353 



aiiiniiils. In oilier words, 1 he fanner will find it necessary 

 to destroy I lie disease-producing organisms in the stables 

 in which diseased animals have been quartered before the 

 stables are used for hcall hy slock. 



Natural agencies. The two agencies of nature that de- 

 stroy many disease-producing organisms arc drying and 

 light. The disease-producing organisms vary widely in 

 their resistance to desiccation. Miost of the non-spore-pro- 

 dncing types endure drying for only a short time, and it is 

 certain that this is one of nature's most effective ways of 

 destroying and limiting the spread of harmful organisms. 



The direct rays of the sun exert a powerful germicidal 

 effect, and are able within a comparatively short time to 

 destroy not only the vegetative cells of the organisms but 

 many of the spores. The action of light as a purifying 

 a-ent is. however, often overestimated. It is effective only 

 when the direct rays of the sun strike the unprotected or- 

 uanism. The action of diffuse daylight is so small as to 

 have no practical importance, and when the organisms are 

 covered with a Ia3 r er of dust, or are embedded in manure or 

 other material, the action of sunlight is of no importance. 



It is certain that ample provision should be made for 

 light in our houses and stables, but not with the idea that 

 disease-producing organisms shall be destroyed, but rather 

 to render ourselves and our domestic animals more resistant 

 in case they arc brought in contact with infectious material. 



Heat is another physical agent that can be used in the 

 destruction of organisms. It is applied either in the form 

 of dry heat, or as steam or hot water, depending on the 

 material to be treated. Here again the resistant powers 

 of the organism must be considered in determining the ex- 

 posure that must be used to be effective. All small objects 

 of wood or iron, and all clothing, can be most easily ren- 

 dered harmless by boiling. In the control of the trans- 



