144 



BACTERIOLOGY. 



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 tem- 

 perature 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 accomplished. When 

 the chamber between the walls is filled with water heat 

 is supplied by a gas-flame placed beneath it. 



Fig. 31. 



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. 31). It is a Bunsen burner pro- 

 vided with an arrangement for automatically turning 

 off the gas-supply and thus preventing accidents should 



