122 



BACTERIOLOGY. 



showing the level of the water between the walls. The 

 object of the water chamber, which is formed by the 

 double wall arrangement, is to insure, by means of the 

 warmed water, an equable temperature at all parts of 

 the apparatus at the top as well as at the sides, back, 

 and bottom, and the apparatus should be kept filled 

 with water, otherwise the purpose for which it is con- 

 structed will not be accomplished. When the chamber 

 between the walls is filled with water heat is supplied 

 from a gas-flame placed beneath it. 



FIG. 28. 



Koch's safety burner. 



The burner employed in heating the incubator was 

 originally devised by Koch, and is known as u Koch's 

 safety burner " (Fig. 28). It is a Bunsen burner pro- 

 vided with an arrangement for automatically turning 



