22 APPLIED BACTERIOLOGY 



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 in a hot-air oven at 133° C. ( = 271° T.), 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° P.), 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 cholera: Asiaticce and the 

 Micrococcus pneumonia crouposce are cases in point. 



By extending the time, a still lower temperature will 

 effect the same result. Chauveau found the anthrax bacillus 

 to be killed by twenty minutes' exposure to a temperature of 

 50° C. ; and Brieger also found that he could sterilise diph- 

 theria cultures by exposure for some hours to the same 

 temperature. 



As already mentioned, there are micro-organisms (gene- 

 rally known as the ' thermophilic ' bacteria) that are able 

 to multiply at a temperature of 65° to 70° C. Miquel, in 

 1881, found a motionless organism in the water of the 

 Seine, which grew in broth at 69° to 70° C. 



Van Tieghem has also discovered several species which 

 grow at about the same temperature. 



