90 INCUBATING OVENS AND THERMO-REGULATORS. 
the pressure of gas, especially, interfere with the maintenance of a 
constant temperature, and for this reason a pressure regulator will 
be required when great precision is desired. That of Moitessier is 
commonly used in bacteriological laboratories (Fig. 60). But for 
most purposes variations éf temperature of 1° to 2° C. are not of 
great importance. For ordinary use a brood oven should be regu- 
lated to about 35° to 37°C. It is best to have a little cylindrical 
screen of mica around the gas jet beneath the incubating oven, for 
the purpose of preventing the flame from being extinguished by cur- 
rents of air (Fig. 61). 
Koch’s ingenious automatic device for shutting off the gas if the 
flame is accidentally extinguished is shown in Fig. 62. 
ese 
Fig. 59, Fig. 60. 
Another form of thermo-regulator, which answers very well, is 
that of Reichert (Fig. 63). In this the gas enters at a and escapes 
at c. The mercury, which fills the bulb, shuts off the gas at the 
point for which the instrument is regulated. By means of the 
screw d the height of the mercury in the tube may be very accu- 
rately adjusted for any desired temperature. 
The regulator of Bohr, shown in Fig. 64, is more sensitive than 
that of Reichert, and rather simpler in construction than the usual 
form shown in Fig. 59. The thermometer bulb a contains only air, 
and the gas which passes through the tube f is shut off at the 
proper temperature by the mercury in the U-shaped tube c. The 
stopcock 6 is left open when the bulb @ is immersed in the water 
