THE INCUBATOlt 43 



H is a lead weight for bringing more or less pressure to 

 bear on the capsule. 



K is the thermometer, the bulb of which is inside and the 

 scale outside the heated chamber. 



The apparatus having been adjusted according to the 

 instructions, the action is as follows : 



The heated products of combustion, not being able to find 

 any exit at the chimney V, pass along the flue L, and, 

 parting with the greater portion of their heat en route, 

 return again to the lantern by a flue behind and parallel 

 with the one seen in the section, and are thence conducted 

 into the open air by a second chimney placed in the lantern 

 a short distance behind the one covered by the damper F. 



The products of combustion continue to move in this 

 direction until the water, and consequently the chamber, 

 are sufficiently heated to distend the capsule. 



When this point is reached, the wire between S and P will 

 be pushed up by the capsule, and the lever will cause the 

 damper to rise more or less off the chimney V. In a short 

 time the damper will be found to hang steadily in one 

 position, and on examining the thermometer at intervals, 

 the inside of the chamber will be found to remain steadily 

 at one temperature. 



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. Hearson 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 



