THE DESTRUCTION OF BACTERIA 



83 



the flame and by the hot air, which, rising from the flame, courses 

 upward within the jacket between the two cases and escapes at the 

 top. To insure absolute sterilization of objects in such a chamber, 

 the temperature should be kept between 150 and 160 C. for at 

 least an hour. In sterilizing combustible articles in such a chamber, 

 it should be remembered that cotton is browned at a temperature 

 of 200 C. and over. .This method is used in laboratories for the 

 sterilization of Petri dishes, flasks, test tubes, and pipettes, and for 

 articles which may be injured by moisture. Both heating and subse- 

 quent cooling should be done gradually to avoid cracking of the 

 glassware. 



Moist Heat. Instruments, syringes, and other suitable objects 

 may be sterilized by boiling in water. 

 Boiling for about five minutes is amply 

 sufficient to destroy the vegetative forms 

 of all bacteria. For the destruction of 

 spores, boiling for one or two hours is 

 usually sufficient, though the spores of 

 certain saprophytes of the soil have been 

 found occasionally to withstand the moist 

 heat at a temperature of 100 C. for as 

 long as sixteen hours. 31 The addition of 



1 per cent of sodium carbonate to boiling 

 water hastens the destruction of spores 

 and prevents the rusting of metal objects 

 sterilized in this way. The addition of 

 carbolic acid to boiling water in from 



2 to 5 per cent usually insures the de- 

 struction of anthrax spores, at least, 

 within ten to fifteen minutes. 



Exposure to live steam is prob- 

 ably the most practical of the methods 

 of heat sterilization. It may be carried out by simple make- 

 shifts of the kitchen, such as the use of potato-steamers or of 

 wash-boilers. For laboratory purposes, the original steaming device 

 introduced by Koch has been almost completely displaced by devices 

 constructed on the plan of the so-called "Arnold" sterilizer (Fig. 

 8). In such an apparatus, water is poured into the reservoir 



FIG. 8. ARNOLD STERILIZER. 



81 Christen, loe. cit. 



