26 



BACTERIOLOGY 



On each side of this tap a lateral tube proceeds in an 

 oblique direction from the horizontal one, to unite at an 

 acute angle with a vertical tube, which contains a vessel 

 drawn out to a capillary termination, and filled with mer- 

 cury in such a way that the convex surface of the metal 

 begins at once to close the lumen of the angle formed by the 

 union of the oblique tubes. If the lower end of the regu- 

 lator is placed in too warm a medium the mercury expands 

 in the capillary, and so permits the gas to pass only 

 through the horizontal tube, where the supply can be still 



Thermometers 



Bearing of lever 



1 I 1 ft 



Wooden casing 



Rubber tube 

 Petroleum lamp 



Fm. YL BAUMEYER'S PETROLEUM IXCUBATOII. 



further reduced by means of the tap. The height of the 

 mercury in the perpendicular tube can be regulated by a 

 screw at the side. 



Petroleum incubator, If the laboratory is not provided 

 with a gas-supply, incubators heated by petroleum can 

 be employed, which are also provided with contrivances 

 arranged for regulating the temperature in the chamber. 

 Such an incubator is made of wood, and contains within it 

 a chest of sheet metal, to the bottom of which is fitted a 

 heating canal furnished with a chimney which runs per- 

 pendicularly up the outside wall (fig. 14). The flame of a 

 petroleum lamp plays into the heating canal and warms 



