138 



BACTERIOLOGY. 



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 

 in all parts of the apparatus at the top as well as at 

 the sides, back, and bottom; the apparatus should be 

 kept filled with water, otherwise the purpose for which 

 it is constructed will not be served. When the cham- 

 ber between the walls is filled with water heat is sup- 

 plied by a gas-flame placed beneath it. 



FIG. 29. 



Koch's safety burner. 



The burner employed in heating the incubator was 

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

 safety burner " (Fig. 29 1 ). It is a Bunsen burner pro- 

 vided with an arrangement for automatically turning 



i There are now many modifications of the original form. 



