INCUBATING OVENS AND THERMO-REGULATORS. 95 
of this simple and convenient incubating oven are manufactured 
by Rohrbeck and by Miincke, of Berlin. The apparatus of D’Ar- 
sonval, and other forms in favor at the French capital, may be ob- 
tained from Wiesnegg, of Paris. The last-named manufacturer 
also supplies the incubating oven and thermo-regulator described by 
Roux (1891). This is shown in Fig. 69. The regulator is formed of 
two metallic bars, one of steel and the other of zinc; these are 
soldered together in the shape of a letter U ; the regulator is seen in 
position in the cut (Fig. 69). The most dilatable metal (zinc) is on 
the outside. When the temperature is raised the arms of the UY ap- 
proach each other, and the reverse when it falls. The method by 
which regulation is effected is shown in Fig. 70. The U-shaped 
regulator is placed vertically, and one of its branches, A, is firmly 
fixed to the wall of the incubating oven ; the other, free arm car- 
ries a horizontal bar which projects through the wall of the incu- 
bator in an opening which permits it to move freely under the influ- 
ence of a change in the temperature within. The end of this 
projecting bar is turned up at a right angle and the screw p passes 
through it ; this can be fixed at any desired point by means of the 
nut e. The end of the screw p rests against the stem of a conical 
brass valve which controls the flow of gas. The valve is closed by a 
spiral spring and opened by the screw p under the control of the 
thermo-regulator. 
In the absence of gas incubating ovens may be heated by a small 
petroleum lamp, and various devices have been invented for control- 
ling the temperature. Reichenbach describes an apparatus for this 
purpose in the Centralblatt fiir Bakteriologie, Vol. XV., p. 847, 
1894. Dr. Borden of the U. 8. Army has also invented a thermo- 
regulator to be used in connection witha petroleum lamp. In the 
absence of any regulating apparatus an incubating oven may be kept 
at a tolerably uniform temperature by personal supervision—adjusting 
the flame of the lamp and its distance from the bottom of the oven ac- 
cording to the changes in the external temperature. For most bac- 
teria a variation of several degrees is not important, so long as the 
temperature is not allowed to rise above 37° to 38° C. The typhoid 
bacillus, the diphtheria bacillus, the anthrax bacillus, the pus cocci, 
and most saprophytic bacteria grow at the ordinary room temperature, 
apd may therefore be cultivated without any form of incubating oven 
or thermo-regulator. 
