DISINFECTION, STERILIZATION AND ANTISEPSIS. 247 



when inoculated upon culture media and remo\cd to a suit- 

 able temperature. 



Light. — Light is injurious to bacteria. Even diffuse day 

 light is harmful, and direct sun light is distructive. Electric 

 arc light is also injurious. The rays which are active are those 

 at the ultra-violet end of the spectrum. 



Heat. — Bacteria are very sensitive to heat. Even tempera-, 

 tures which are far short of burning or charring kill the bac- 

 teria very promptly. The vegetative cells are for the most part 

 destroyed by temperatures around 60° C. in a comparatively 

 short time, — ten or fifteen minutes. Spores are much more 

 resistant to heat, some of these withstand the temperature of 

 boiling water for a few minutes and some even for an hour 

 or more. 



Otiier Physical Agents. — Pressure, Rontgen rays, electric 

 currents are not injurious to the bacteria. 



Chemical Disinfectants. 



The most efficacious method of disinfection is by heat applied 

 as steam preferably under pressure. This mode of disinfec- 

 tion is applicable to bed clothing and underclothing, but it is 

 not applicable to rooms and the like, and for this purpose 

 recourse is had to various chemical agents. The list of sub- 

 stances possessing germicidal properties is large, but not all of 

 these are available for practical disinfection. At one time the 

 efhcacy of chemical disinfectants was probably overrated. 

 At all events, in practice much more drastic measures than 

 would be indicated by laboratory experiments should be 

 employed. In fact, the questions involved and the problems 

 to be solved in practical disinfection are often very different 



*For fuller details on this subject consult Rosenau. Disinfection and Dis- 

 infectants. 1902. Also Gotschlich. Disinfection. KoUe and Wassermann. 

 Handbuch der pathogenen Mikroorganismen. IV. Teil. i, 1904. Harrington 

 and Walker. The Boston Medical and Surgical Journal. April 23, 1903. 

 Vol. CXLVIII., No. 17. Gunther, loc. cit. 



