732 



A MANUAL OF BACTERIOLOGY 



A glass tube of special form is employed (Fig. 67) ; this consists 

 of an expanded portion (A) about 15 cm. long and 4-5 cm. in 

 diameter ; one end of this is contracted so as to form a neck 2-5 cm. 

 in diameter and in length ; to the other end is fused a glass tube 

 (B c) 15 cm. long and 0-5 cm. in diameter. The neck of the 

 tube is plugged with cotton-wool, and two cotton-wool or 

 better, glass-wool plugs are inserted in the narrow tube, one 

 at its open end, the other (c) about 6 to 8 cm. 

 from the wide part. The whole is then steri- 

 lised. When cool, the narrow part of the tube, 

 from its origin at the wide part down to the 

 first plug (c), is filled with powdered cane- 

 sugar (No. 50, B.P. gauge) which has been care- 

 fully dried and sterilised at 120-130 C. The 

 tube is again sterilised at 120-130 C. for two 

 or three hours, the greatest care being taken 

 not to melt the sugar. After sterilisation the 

 tube is ready for use. The wool plug is 

 removed from 'the mouth and a measured 

 volume of air is aspirated through the layer 

 of powdered sugar by means of a small hand 

 air-pump, the volume of air being measured 

 by the displacement of water in a flask. 

 Having taken the sample (5 to 20 litres), the 

 wool plug is replaced in the neck. The pow- 

 dered sugar is then shaken down into the 

 wide part of the tube (A), and 15 c.c. of melted 

 sterile nutrient gelatin are poured in. The 

 powdered sugar readily dissolves in the melted 

 gelatin, and when solution is complete a 

 roll-culture is made in the tube, just as in 

 Esmarch's method (p. 99). The tube is then 

 placed in an incubator at 20 C., and the 

 colonies are allowed to develop. 



In both Frankland's and Sedgwick and Tucker's methods 

 the sugar, after powdering and sifting and before introducing 

 into the tubes, should be thoroughly dried by keeping in the 

 warm incubator for several days with occasional stirring. Unless 

 this be done, the sugar is apt to cake and discolour during 

 sterilisation, 



.Fir;. 67. Sedgwick 

 and Tucker's tube 



for air analysis. . 



