244 BACTERIOLOGY. 



der to obtain results. The apparatus employed for this 

 purpose is known as an incubator or thermostat. It is made 

 of heavy copper and has double walls. The space between 

 these, which should be as large as possible, is filled with 

 distilled water. In form the thermostat may be oblong, 

 square or oval. Fig. 36 shows an excellent thermostat of 

 oval form. 



FIG. 36. The incubator or thermostat. 



It is desirable that the incubator should have as much 

 available space as possible for dishes, flasks, tubes, etc. 

 The apparatus as ordinarily made is quite expensive. Any 

 one with a little ingenuity can plan out a double -walled box 

 and have an incubator made by a tinsmith which will answer 

 all ordinary purposes. It should have a double door or lid, 

 and it is advisable, though not necessary, that the side and 

 top should be covered with asbestos or felt. The top should 

 be provided with an opening which communicates with the 

 water compartment and serves to hold a thermo-regulator. 



