INCUBATORS 



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walls is heated by means of a small burner, the gas 

 supply for which passes through some form of regulator 

 inserted in the water, so that the temperature, indicated 

 by a thermometer inserted through a hole in the top, 



FIG. 13. Hearson's incubator. 



can be kept constant. The regulator is usually a mercurial 

 one, such as Page's or Reichert's, the principle of its 

 action being that as the temperature rises the mercury 

 expands and at a certain point cuts off the greater part 

 of the gas supply, only sufficient gas then passing to keep 

 the flame of the burner alight. This point can be varied 



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