THE CULTIVATION OF MICRO-ORGANISMS 



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 

 cooling the mercury falls and allows gas to flow again through 

 the larger opening. In this way the supply of gas is made large 

 whenever the temperature is a little below the 

 desired temperature and very small whenever 

 the temperature rises above that point, and the 

 temperature varies within a slight range. The 

 Reichert regulator is designed to operate ac- 

 cording to these principles, and various modi- 

 fications of this regulator are on the market. 

 In many of these instruments the larger supply 

 is only imperfectly shut off at the desired tem- 

 perature, and, where the weight of the mercury 

 is relied upon to stop this opening, the gas may 

 often bubble out through it unless special pre- 

 cautions are taken to regulate the pressure of 

 the gas supply. 



A modification of this type of regulator 

 devised by Mac Neal 1 overcomes this difficulty 

 (see. Fig. 48). The inlet tube A leads through 

 the wall of the chamber D, to which it is fused, 

 into an inner upright tube, B C . Near the upper 

 end of this upright is a small opening, O, which allows the minimum 

 supply of gas to pass to the burner to avoid extinction of the flame. 

 The lower end of this upright tube fits quite closely the bottom of 

 the chamber D, around the opening leading into the capillary 

 tube, EF. This end is adjusted so close to the bottom that mer- 

 cury will not pass through between inner and outer tube at less 

 than twenty millimeters mercury pressure, yet not so close but 

 that an abundant supply of gas may pass. The proper adjust- 

 ment of this part must be thoroughly tested before the instrument 

 leaves the factory. The upper end of the upright, BC, is closed 



1 The Anatomical Record, August, 1908, Vol. II, No. 5. 



FIG. 47. Reichert's 

 gas-regulatcr. 



