FRAENKELS TUBE 



91 



tion by the inrush of air to fill the vacuum), make a file mark in 

 the centre of the tube, and carry the crack round with a red-hot 

 wire. The tube can then without difficulty be divided in two, and 

 any desired colonies picked out with a sterile platinum needle 

 for examination or culture. 



7. Fraenkel's tubes for anaerobic cultivation in liquid 



media- 

 Take an ordinary large sized and sufficiently strong test-tube and 



plug with an india-rubber stopper pierced with two holes. Through 



one of these introduce a glass tube, bent 



at right angles and of such a length that 



one extremity reaches almost to the 



bottom of the test-tube, whilst the other 



projects about i inch above the stopper, 



with a right-angled projection of some 



2\ to 3 inches. A similar tube, but of 



such a length that it will just project 



beyond the bottom edge of the stopper, 



is inserted through the second hole. 



Before inserting the tubes make a con- 

 striction in the right-angled return of 



each, plug with cotton-wool and, turning 



the ends in the Bunsen flame, partially 



close the openings in order to prevent 



the possible exit of the cotton-wool plug. 

 Introduce a sufficient quantity of 



medium into the tube,^ replace the india- 

 rubber stopper with its tubes, and 



sterilise in the ordinary manner. When 



required for use, liquefy the medium, in- 

 oculate with a trace of the culture to be 



studied, thoroughly incorporate, make an air-tight joint with benzole 



or paraffin, and connect the longer tube with the hydrogen apparatus. 

 Pass a current of hydrogen under pressure {see p. 82) through 



the medium for a sufficient length of time to expel all the contained 



oxygen, and seal off both tubes (the exit tube first) in the flame, or 



screw down the pinchcocks on india-rubber fittings as shown on 



Fig. 25. Incubate at 22°, or lower temperature. 



^ To avoid excessive frothing when subsequently passing a current of 

 hydrogen through the medium, it is well to place one drop of sterile oil on the 

 surface of the gelatine. 



\o 



Fig. 25. — Fraenkel's tube. 



