THE BA CTERIOLOGICA L LABOR A TOR Y 41 



mercury is forced up by means of the screw in the 

 lateral arm, until it closes the orifice, at the extre- 

 mity of the vertical portion of the T piece. The 

 gas which passes through the lateral orifice is suffi- 

 cient to maintain the apparatus at the required 

 temperature. If the temperature of the incubator 

 falls the mercury contracts, and the gas passing 

 through the terminal orifice of the T piece, increases 

 the flame of the burner, and the temperature is 

 restored.' Page's regulator resembles somewhat the 

 regulator just described : both are simple and useful 

 forms for the bacteriological laboratory. By such 

 devices the various incubators, may be maintained 

 at a temperature which is almost constant; the 

 slight differences (say of one or two degrees Centi- 

 grade) are due to the variations in the pressure of 

 the gas supply ; but this inconstancy is remedied by 

 first passing the gas through a pressure - regulator 

 (such as Moitessier's). 



In addition to the above-mentioned regulators, 

 there are two forms which are worked by the agency 

 of the electric current. Babes' 1 and Abel's 2 are 

 thermo-electric regulators ; the latter being repre- 

 sented in Fig. 16. These are useful regulators ; but 

 for general work those of Keichert and Page are 

 specially recommended. 



Cultivation Tubes, etc. Fig. 17 represents an im- 

 portant series of glass tubes, flasks, etc., used in 

 the cultivation of microbes in liquid media. These 



1 Centralblatt fur Bakteriologie und Parasitenkunde, 1888. 



2 Ibid,, 1889, p. 707. 



