THE CULTIVATION OF MICRO-ORGANISMS 



121 



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 according to 

 these principles, and various modifications of 

 this regulator are on the market. In many 

 of these instruments the larger supply is only 

 imperfectly shut off at the desired temperature, 

 and, where the weight of the mercury is reHed 

 upon to stop this opening, the gas may often 

 bubble out through it unless special precau- 

 tions are taken to regulate the pressure of the 

 gas supply. 



A modification of this type of regulator 

 devised by Mac NeaP overcomes this difiiculty 

 (see Fig. 50). The inlet tube A leads through 

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

 into an inner upright tube, BC. Near the 

 upper end of this upright is a small opening, 

 0, 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 bot- 

 tom of the chamber D , around the op ening leading into the capillary 

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

 cury will net pass through, between inner and outer tube at less 

 that twenty millimeters mercury pressure, yet not so close but 

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

 ment of this part must be throughly tested before the instrument 

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

 by a ground glass stopper, which also closes the top of the outer 

 chamber, D. In the ground surface of this stopper a gamma- 

 shaped (r) groove is cut, the vertical limb extending from the 



1 The Anatomical Record, August, 1908, Vol. II, No. S- 



Fig. 49. — Reichert's 

 gas-regulator. 



