2l8 INCUBATORS 



most essential portion of the incubator, as upon its 

 efficient working depends the maintenance of a con- 

 stant temperature in the cultivation chamber. It is 

 also used in the fitting up of water and paraffin baths, 

 and for many other purposes. 



Of the many forms and varieties of thermo-regulator 

 (other than electrical), two only are of sufficiently 

 general use to need mention. In one of these the flow 

 of gas to the gas-jet is controlled by the expansion or 

 contraction of mercury within a glass 

 bulb ; in the other, by alterations in 

 the position of the walls of a metal- 

 lic capsule containing a fluid, the 

 boiling-point of which corresponds 

 to the temperature at which the in 

 cubator is intended to act. They 

 are: 



(a) Reichert's (Fig. 115), consists of 

 a bulb containing mercury which is 

 FIG. 115. Reichert's to be suspended in the medium, 

 thermo-regulator. w h e ther air or water, the temperature 

 of which it is desired to regulate. Gas enters at A, and 

 passes out to the jet by B. As the temperature rises 

 the mercury expands and cuts off the main gas supply. 

 As the temperature falls the mercury contracts and re- 

 opens the narrow tube C. By means of a thumbscrew 

 D (which mechanically raises or lowers the column of 

 mercury irrespective of the temperature) and the aid 

 of a thermometer the apparatus can be set to keep the 

 incubator at any desired temperature. With this form 

 a special gas burner is required, with separate supply of 

 gas to a pilot jet at the side. 



(b) Hear son's capsule regulator consists of a metal cap- 

 sule hermetically sealed and filled with a liquid which 

 boils at the required temperature, this is adjusted in the 

 interior of the incubator. Soldered to the upper side of 

 the capsule is a thick piece of metal having a central 



