ACTION OF HEAT 23 



and the Micrococcus piiaumonice 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 sterilize 

 diphtheria 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. 



With regard to the resisting power of ' spores ' to moist 

 heat, those of many pathogenic bacteria are quickly 

 kUled by a very short exposure to 100° C. ( = 212° F.). 

 There are others, such as those of tuberculosis, infantile 

 diarrhoea (Fliigge), puerperal fever, and symptomatic 

 anthrax, which, after being dried, may resist boiling for 

 many hours. Spores of certain non-pathogenic species 

 may resist the boiling-water temperature (100° C. = 212° F.) 

 for as much as sixteen hours. In view of the fact that the 

 existing organisms of some of the most dangerous infectious 

 diseases, such as small-pox and scarlet fever, are as yet 

 undiscovered, no distinction can be drawn for practical 

 purposes between the resistance of pathogenic and that 

 of non-pathogenic organisms, and measures of disinfection 

 must, so far as possible, be chosen so as to be capable of 

 destroying the most resistant organisms. 



Steam for disinfecting purposes must always be saturated, 

 and not superheated ; that is to say, it must not be raised 

 above the temperature at which under the existing pressure 



