THE INCUBATOR 49 



ing the utmost changes of temperature occurring in these 

 latitudes, nor will very great alterations in the size of the 

 lamp-flame seriously alter the results. 



37. The milled head-screw P must not be turned, after 

 the first adjustment, during the whole time that the incu- 

 bator is in use. 



Observe the temperature before opening the door ; observa- 

 tions taken afterwards are worthless. 



The Cool Incubator. — It must be clearly understood that the 

 ordinary incubator with the Excelsior valve is only suitable 

 for temperatures at least 5° F. above the temperature of the 

 room in which the incubator is used. In order to render 

 bacteriological investigation by means of gelatine tubes and 

 plates possible during hot summers and in tropical climates, 

 Messrs. Hear son have devised a cool chamber or incubator in 

 which ice is used. It consists of a water- jacketed chamber, 

 similar to that already described, surmounted by a vessel, B, 

 which contains ice, the whole apparatus being surrounded by 

 a thick layer of non-conducting material and wood to protect 

 it as far as possible from the effects of external influences. 



The regulation of temperature within the chamber is 

 effected by a small stream of water which runs con- 

 tinuously through the apparatus in one of three directions, 

 the choice being automatically determined by a thermo- 

 static capsule. 



On the top of the apparatus is a lever plate and lever, M, 

 similar to the one used in the lamp incubator already 

 described, only in this case the damper is dispensed with. 

 A bracket screwed to this plate supports a vertical shaft, 

 pivoted on centres at the top and bottom, which carries a 

 horizontal tube, C. 



In the incubating chamber is a capsule in a holder, sup- 

 ported by a tube screwed to the lever plate. 



A stiff wire communicates the motion of the capsule (as 



4 



