152 



LABORATORY EXERCISES IN BACTERIOLOGY. 



tially an inclosure the temperature of which is maintained at a uniform degree by artifice 

 of some sort. The form most efficient and usually used in the laboratory is a chamber 

 surrounded, except on the side of the door, by a water-bath (Fig. 44), the source of 

 heat being a small, constant flame adjusted beneath the apparatus. For better preserva- 

 tion of uniformity there is usually an incasement of asbestos felt on the exterior, except 

 over the bottom where the flame is applied. A double door, the inner portion of glass 

 (for inspection of the interior of the chamber without exposure) and the outer of metal 



FIG. 44. SECTIONAL VIEW OF INCUBATOR. 



A. Incubator chamber. B. Ventilation wall. C. Water-bath. D. Thermometer. . 

 Thermostat. F. Microchemical burners. G. Felt covering of incubator. H. Water 

 gauge. 



and felt, allows access to the interior; and a small opening is provided through the 

 top for accommodation of the thermometer, which extends into the interior. Several 

 openings at the top lead into the interior for ventilation, and into the water-bath 

 for filling, cleaning, and the introduction into the warm water of a temperature regulator 

 (thermostat}. This last device is an appliance for the automatic regulation of the size 

 of the flame beneath the incubator, causing it to decrease as the warmth of the water 

 increases, or to increase as the temperature of the water falls. There are a number 

 of forms applicable to gas or to lamp flames, as well as special devices for the regu- 



