22 BACTERIOLOGY 



advantage of the rise and fall of mercury, and, in case the 

 opening for the passage of the gas should become com- 

 pletely closed, he devised a safety aperture which allows 

 just so much gas to pass through as keeps the flame from 

 being extinguished. Various thermo-regulators have been 

 constructed on this principle. 



Schenk's thermo-regulator, A regulator in use for the 

 incubator in the author's Institute is constructed as fol- 

 lows (it can be procured from Siebert, 19 Alserstrasse, 

 Vienna) : A piece of glass tubing is sealed into a vessel of 

 glass shaped like a test-tube, in such a way that one end 

 of the former, which is widened out, adheres air-tight to 

 the sides of the latter vessel, while the other end reaches 

 nearly to the bottom. If now mercury be poured into this 

 apparatus a portion of it will sink through the narrow tube 

 to the bottom of the wider vessel, while the rest fills the small 

 tube and extends above it to such a height as to allow of the 

 test-tube being closed with a cork which is perforated with 

 one aperture. The air contained in the apparatus renders it 

 more sensitive by causing the mercury to rise and fall more 

 rapidly with the alterations in its volume produced by 

 variations of temperature. Into the cork is fitted a second 

 glass tube, which is expanded in its upper half, this ex- 

 panded part being closed by a cork perforated twice and 

 traversed by two glass tubes bent at right angles. One 

 of these, which extends down as far as the constriction 

 of the upper vessel, is ground away obliquely at the end, 

 and has a minute- safety aperture in one side ; the other is 

 simply a bent tube reaching to the lower surface of the 

 cork only. 



In actual use the apparatus is interposed between the 

 supply-pipe of the gas and the burner by attaching to each 

 angular tube a piece of india-rubber pipe, on the one side 

 from the burner, on the other from the gas-tap. The test- 



