22 APPLIED BACTERIOLOGY 



Koch and Wollffhiigel, in 1881, made a thorough investi- 

 gation of this subject. A large number of pathogenic and 

 non-pathogenic organisms were tested, with the following 

 results : 



A temperature of 78° to 123° C. (=172° to 253° ¥.), main- 

 tained for over an hour, was found not to kill, and it was 

 found necessary to employ a temperature of 120° to 128° C. 

 ( = 248° to 262° F.) for at least an hour and a half to insure 

 the complete destruction, in the absence of spores, of all of 

 the species tested. The spores of Bacillus anthracis and 

 Bacillus subtilis resisted this temperature, and required to 

 insure their destruction a temperature of 140° C. ( = 284° F.) 

 maintained for three hours. This temperature is injurious 

 to most articles requiring disinfection, such as bedding and 

 clothing. But the lower temperature (120° C. = 248° F.), 

 which destroys germs in the absence of spores, can be 

 employed for disinfecting articles soiled with the discharges 

 of patients with cholera, typhoid, or diphtheria, as the 

 specific organisms of these diseases do not form spores. 

 In practical disinfection it is necessary to remember that 

 dry heat possesses but little power of penetration. In the 

 experiments of Koch and Wollffhiigel, it was found that 

 registering thermometers, placed in the centre of folded 

 blankets and various packages, did not indicate a tem- 

 perature sufficiently high to destroy germs, even after three 

 hours' exposure m a hot-air oven at 138° C. ( = 271° F.), and 

 above. 



Moist Heat.— The thermal death-point of bacteria in the 

 absence of spores is comparatively low when exposed to 

 moist heat. Thus, all the pathogenic organisms as yet 

 isolated are killed, when free from spores, by a temperature 

 of 60° C. ( = 140° F.), or below. Some of them fail to 

 grow after an exposure to as low a temperature as 50° C. 

 for two or three minutes. The Spirillum cholerce Asiaticm 



