76 MANUAL OF BACTERIOLOGY. 



heat, such as felt or asbestos. At one side is a door, which 

 is also double. The inner door is of glass, the outer door 

 is of copper covered with asbestos. At one side is a gauge 

 which indicates the level at which the water stands in the 



Fig. 22. — Incubator. 



water-jacket. The roof is perforated with several holes, 

 some of which permit the circulation of the air in the air- 

 chamber inside the box; some of them enter the water-jacket. 

 A thermometer passes through one of these holes into the 



