THE CULTIVATION OF BACTERIA. 



8 9 



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 interior of the air-chamber, and often another into 

 the water standing in the water-jacket. A gas-regulator 

 passes through another hole, and is immersed in the water 



FIG. 23. FIG. 24. 



Reichert's Gas-regulator. Mercurial Gas-regulator, a. Cham- 



ber containing volatile hydrocarbon. 

 b. Capillary opening. 



standing in the water-jacket. There are various forms of gas- 

 regulators more or less complicated. In general they consist 

 usually of a tube containing mercury ; into this tube are two 

 openings, one for the entrance and the other for the exit of 

 gas. The gas enters through a small tube, which is cut off 

 diagonally at the bottom, and which projects into the sur- 

 face of the mercury. Heating the water in the water-jacket 



