METHODS OF CULTURE. 



41 



and | foot deep. In them, glass-ware, cotton, and paper can be 

 sterilized. When the cotton is turned slightly brown it usually 

 denotes sufficient sterilization. All instruments, where prac- 

 ticable, should be drawn through flame of alcohol lamp or Bun- 

 sen burner. 



Moist Heat. Steam of 100 C. in circulation has been shown 

 to be a very effective application of heat. 



Koch's Steam-chest, The best 

 way of obtaining circulating 

 steam is by aid of Koch's appa- 

 ratus. This consists of a cylin- 

 drical tin chest about 2 feet 

 high and about | foot in diame- 

 ter ; divided in its interior by a 

 perforated diaphragm, a, an up- 

 per chamber for the, c, steam and 

 a lower one for water, 6. Two 

 or more gas-burners placed under- 

 neath the chest, which stands on 

 a tripod, supply the heat. In the 

 cover is an opening for a ther- 

 mometer. The chest is usually 

 covered with felt. When the 

 thermometer registers 100 C,, 

 the culture medium or other sub- 

 stance to be sterilized is placed 

 in the steam and kept there 10 to 

 15 minutes, or longer, as required. 



The autoclave of Chamberland 

 allows a temperature of 120 C, 

 to be obtained, and is much used 

 in Pasteur's laboratory. 



Instead of sterilizing for a long 

 time at once, successive steriliza- 

 tion is practised with nutrient 

 media, so that the albumen will 

 not be too strongly coagulated, 

 three days in succession. 



FIG. 12. 



Koch's Steam-chest. 



Fifteen minutes each day for 



