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BACTERIOLOGY 



the water-jacket. There are various forms of gas-regulators 

 more or less complicated. The simplest and least expensive 

 thermo-regulators for gas are made of glass and filled with mercury 

 or with mercury and some lighter liquid, the heavy mercury 



Pig. 48. — Incubator. 



serving to close the chief source of gas supply when the desired 

 temperature has been attained, while a minute opening at another 

 point remains open to furnish sufficient gas to keep the flame 

 alight, but not sufficient to maintain the temperature. Upon 



