THE PREPARATION OF CULTURE MEDIA 3D 



in the usual way. Tlie living material which is to be 

 anaerobically cultivated is introduced on a platinum- 

 needle into the melted gelatine, and thoroughly distri- 

 buted throughout the latter. The cotton-wool plug is 

 now removed and immediately replaced by an india- 

 rubber stopper, the two perforations in which are fitted 

 with glass tubes, one of which only just opens into the 

 test-tube, whilst the other is long enough to reach 

 nearly to the bottom of the latter. Each of these glass 

 tubes is constricted above the india-rubber stopper, 

 and beyond these constrictions are placed small plugs 

 of sterile cotton-wool ; this india-rubber stopper fitted 

 with its glass tubes is sterilised in the steamer, and is 

 not removed from the latter until the moment when 

 required for placing on the test-tube. This having been 

 done, the longer glass tube is connected with a Kipp's 

 or other generator of hydrogen gas, whilst to the outside 

 of the shorter glass tube is attached a piece of narrow 

 india-rabber tubing about one foot in length, which is 

 allowed to hang down loosely. A fairly rapid current 

 of hydrogen is then bubbled through the gelatine, which 

 is kept fluid by immersing the test-tube in a beaker of 

 water at 30° C. The hydrogen escapes through the long- 

 piece of india-rubber tubing attached to the shorter 

 glass tube which passes through the india-rubber stop- 

 per. When the gas has been passing for ten to fifteen 

 minutes it is stopped, and the two glass tubes are rapidly 

 sealed before the blowpipe at the constricted points 

 referred to above. The india-rubber stopper is then 

 thickly coated with melted paraffin so as to render it 

 perfectly gas-tight, and the tube is rotated in a hori- 

 zontal position in cold water until the gelatine con- 

 geals in a uniform film over the inner walls, as in 

 the ordinary Esmarch-tube (see p. 35). The colo- 

 nies of those organisms capable of growing in the 



