756 A MANUAL OF BACTERIOLOGY 



death of all micro-organisms exposed to it, within the ten minutes 

 in these standard conditions. 



LIGHT is not used directly for disinfection, but indirectly 

 in nature and in our homes may not be an unimportant 

 factor. It has previously been referred to at p. 28. Sun- 

 light, and artificial light rich in violet and ultra-violet 

 radiations, such as that emitted by a quartz mercury 

 vapour lamp, are efficient germicides. The latter was 

 tested by Barnard and the author with excellent results, 

 but, unfortunately, the germicidal rays have no power of 

 penetration and are stopped even by thin glass. 



DESICCATION, although one of Nature's methods of 

 disinfection, is riot made use of to any extent by man 

 except as an inhibitory agent for the preservation of many 

 articles of food. Shattock and Dudgeon found that many 

 bacteria, e.g. E. coli and B. typhosus, rapidly succumb to 

 complete desiccation, but B. pyocyaneus maintained its 

 vitality for two years under these conditions. 



FILTRATION is a method of disinfection by exclusion, 

 and in the form of sand filtration and filtration through 

 a porous candle, as in the Berkefeld and Pasteur-Cham - 

 berland filters, is made use of for the sterilisation of water 

 and other fluids. 



CHEMICAL DISINFECTANTS. A large number of chemical 

 substances variously known as germicides, antiseptics, 

 disinfectants, deodorants, etc., have the power of inter- 

 fering with, or masking the results of, the vital activities 

 of micro-organisms. Germicides are substances which 

 kill bacteria or germs ; antiseptics, by inhibiting bacterial 

 development, prevent sepsis or putrefaction ; and by 

 " disinfectant " is meant a substance which prevents the 

 action of, or destroys, infective matters, while deodorants 

 destroy or absorb foul-smelling gases the result of putre- 

 factive and similar processes. All germicides are disin- 

 fectant and antiseptic, but many antiseptics, though 



