THE CULTIVATION OF BACTERIA. 



tubes is cut off just underneath the stopper, and the other 

 is long enough to project nearly to the bottom of the cul- 

 ture-tube. The horizontal projecting parts are drawn to a 

 small caliber at some point, although not quite closed, to fa- 

 cilitate sealing later on. Through the longer of these tubes 

 hydrogen gas is passed until the atmosphere inside of the 

 culture-tube is pure hydrogen, entirely free from mixture with 

 air. The horizontal parts of the small 

 glass tubes projecting from the stopper 

 are then sealed in the flame at the 

 places where they were previously drawn 

 out to a small caliber, and the tubes are 

 thus closed. (Fig. 27.) 



The stopper should be surrounded 

 with melted paraffin. A tube prepared 

 according to this plan may, if desired, be 

 converted into an Esmarch roll-tube. 

 The hydrogen is generated according to 

 the common method with pure zinc and 

 pure sulphuric acid, 25 to 30 per cent. 

 The precautions advised by chemists 

 for the generation of hydrogen must be 

 carefully followed, because when hydrogen 

 mixed with oxygen or air is ignited a 

 violent and disastrous explosion may p^,, 

 occur. 



The well-known Kipp's generator 

 may be used. First let the reservoir fill with hydrogen; 

 then allow its contents to escape. This should be repeated, 

 after which some of the hydrogen may be collected in an 

 inverted test-tube under water. When this sample is ignited, 

 it should burn without any explosion; otherwise the hydro- 

 gen is not yet ready to use. The hydrogen should bubble 

 through the medium five minutes or more. 



27.- 



■CULTIVATION 



OF Anaerobes by 

 Frankel's Method. 



