INCUBATOR 



21 



fixed to the outside, indicates the height of the water. 

 The heating of the apparatus is carried on by small gas- 

 flames (micro-burners), protected from draughts by cylinders 

 of mica. The incubator serves the purpose of keeping- 

 cultures of micro-organisms at a fixed uniform temperature 

 in cases where they will not grow at higher or lower degrees 

 of heat (fig. 11). 



In order to secure an even temperature a thermo- 

 regulator is employed, which (with the very slightest varia- 



Felt coating 



Thermometer 



- Water-gauge 



FIG. 11. INCUBATOR. 



tions) maintains the thermometer at a constant temperature. 1 

 It has the function of increasing the flame when the tempera- 

 ture falls, and diminishing it when the temperature rises by 

 regulating the supply of gas. For this purpose Bunsen took 



by means of double doors, one or both of which is made of glass, in order 

 that the cultures, &c., in the interior may be observed without the loss of 

 heat which must necessarily follow the opening of the apparatus. The two 

 instruments are, however, identical in principle and in all other essential 

 details.] TK. 



1 [The terms ' room temperature,' * ordinary temperature,' &c., which 

 will be frequently met with in the following pages, denote a temperature of 

 about 20 C., while by ' incubation temperature ' is meant one of about the 

 heat of the human body, i.e. 37 C. (German, Zimmertemperatur and Brut- 

 temperatur respectively). The Incubator is usually kept at the latter tem- 

 perature.] TK. 



