132 3Ianual of Veterinary Microbiology. 



For cultivation at 20° it is sufficient to place the 

 inoculated media in an ordinary room ; this room 

 should be heated in winter, and in summer, on the 

 other hand, should be protected from a too free en- 

 trance of the sun's rays. If necessary, a room can 

 be provided with double windows and padded door, 

 in which is kept a stove receiving gas from a thermo- 

 regulator placed in the room ; a constant temperature 

 can thua be obtained. 



When the cultures require a temperature of from 

 30° to 40°, we have recourse to special ovens. These 

 are air ovens in which a suitable temperature is main- 

 tained. 



Culture ovens are of various forms and sizes. 

 They may have single or double walls; in the latter 

 case the space between these walls contains a layer 

 of water. They are, further, furnished with an ar- 

 rangement which permits of the renewal of the in- 

 terior air. These ovens may be regulated for differ- 

 ent temperatures; usually they are heated to 39° C. 

 Culture ovens have also been constructed, the tem- 

 perature of which varies at different levels but re- 

 mains constant for each of these. 



Two principal conditions must be fulfilled in order 

 to maintain a constant temperature; the loss of heat 

 must be reduced to a minimum and be invariable, 

 and the heat communicated to the apparatus must be 

 equal to the heat lost. The first condition is obtained 

 by surrounding the ovens with a body which is a bad 

 conductor of heat, such as felt, sometimes by a 

 double wall and a double door, and by placing them 

 in a room kept at a uniform temperature. As to the 

 second, it requires a more complicated arrangement; 



