164 BACTERIOLOGY 



Gas-pressure Regulators. A gas-pressure regulator is some- 

 times intervened between the gas-supply and the thermo- 

 regulator. This apparatus has for its object the maintenance 

 of a constant pressure of the gas going to the thermo-regu- 

 lator. There are several forms of regulator in use, but they 

 do not accomplish the object for which they are designed. 



The instrument most commonly employed, the apparatus 

 of Moitessier (Fig. 31), is based on somewhat the same 

 principles as the large regulators seen at the manufactories 

 of illuminating-gas. Such apparatus act very well when 

 employed on the large scale, as one sees them at the gas- 

 works; but when applied to the limited and sudden fluctua- 

 tions seen in the gas coming from an ordinary gas-cock 

 are practically useless. They are too gross in their con- 

 struction, and act only under comparatively great and 

 gradual fluctuations in pressure. If a good form of thermo- 

 regulator be employed, there is no necessity for the use of 

 any of the pressure-regulators thus far introduced. 



