STERILIZATION AND DISINFECTION. 



93 



has introduced little paper caps with which the cotton 

 stoppers are protected from the dust. These are easily 

 made by curling a small square of paper into a "cornu- 

 copia, ' ' fastening by turning up the edge or putting in a pin. 

 The paper is placed over the stopper before the sterilization, 

 after which no contamination of the cotton can occur. 



Sterilization of Culture-media. As almost all of the 

 culture-media contain about 80 per cent, of water, which 

 would be evaporated in the hot-air closet, so that the 

 material would be destroyed, hot-air sterilization is not 

 appropriate for them. Sterilization by streaming steam 

 is the best and surest method. The prepared media are 



placed in flasks or tubes care- 

 fully plugged with cotton and 

 previously sterilized with dry 

 heat, and then sterilized in what 

 is known as Koch's steam appa- 

 ratus (Fig. 9) or in Arnold's 



FIG. 9. Koch's steam sterilizer. 



FIG. 10. Arnold's steam sterilizer. 



steam sterilizer (Fig. 10), which is more convenient and 

 more generally useful. 



The temperature of boiling water, 100 C., does not 



