132 BACTERIOLOGY. 



and the thermo-regulator. This apparatus has for its 

 object the maintenance of a constant pressure of the 

 gas going to the thermo-regulator. There are several 

 instruments of this form in use, but they do not ac- 

 complish the object for which they are designed. 



The instrument most commonly employed, the appa- 

 ratus of Moitessier (Fig. 33), is based on somewhat the 

 same principles as the large regulators seen at the manu- 

 factories 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 fluctuations seen in the gas coming from an 

 ordinary gas-cock are practically useless. They are too 

 gross in their construction, and act only under compar- 

 atively 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. 



