114 BACTERIOLOGICAL ANALYSIS LESSON 



(5) Clamp at C as tightly as possible, so as to prevent 

 air from entering into the flask (A). 



It is advisable to smear all the fittings and joints 

 and the end of the india-rubber tube below C with 

 hard paraffin. 



(6) Place the flask in the cool incubator and watch for 

 the appearance of colonies in the gelatine. If such appear, 

 carefully melt the gelatine at 38 C. and shake the flask 

 gently, and with a sterile pipette fill each of 5 to 10 

 tubes with 10 cc. of the gelatine. 



(7) Prepare roll tubes of them in the ordinary manner. 

 These should be loosely plugged. 



(8) Place these tubes in a sterilised, large, wide-necked 



bottle containing some freshly prepared 

 solution of pyrogallic acid in caustic 

 potash 1 (Fig. 11). A little moistened 

 sand (s) should previously be placed in 

 the flask, for the tubes to rest on. 



(9) Close the wide neck of the flask 

 with a perforated india-rubber stopper (i) 

 and insert a bent tube (t) through the 

 stopper, which must not extend far into the bottle. 



(10) Connect the bent tube with the air-pump and 

 exhaust the bottle thoroughly. 



(11) When all the air has been exhausted, clamp tightly 



1 This is made by using 10 cc. of a 10 per cent solution of caustic 

 potash for every gramme of pyrogallic acid required. The caustic 

 potash solution must not be added to the pyrogallic acid until just 

 before closing the flask. 



