EXAMINATION OF AIR 



607 



plugged end, which is connected by stout rubber tubing to aspi- 

 rating flasks such as are used in Hesse's apparatus. The tube is 

 clamped horizontally to a retort stand, and by attaching the second 

 flask to a small hand exhaust-pump, the water can be syphoned 

 over from the first flask, a corresponding volume of air passing 

 through the tube. When the desired volume of air has been 

 aspirated through the tube, it is disconnected j-rt^ 



and placed in another sterile tin box. As many 

 tubes as desired can be employed to control 

 one another or to examine the air in different 

 localities and under different conditions. All 

 the samples having been taken, the tubes are 

 manipulated on returning to the laboratory. 

 The tubes, as before, being handled by the 

 ends only, a file-mark is made across the centre 

 of each tube, which is then broken in half and 

 the plugs of glass-wool and sugar are shaken, 

 or pushed by means of a sterile wire, into a 

 sterile flask of about 250 c.c. capacity. Into 

 this 10 or 15 c.c. of liquefied sterile nutrient 

 gelatin are then introduced ; the sugar dis- 

 solves, the glass-wool becomes disintegrated, 

 and a roll-culture is made on the walls of the 

 flask, which is incubated at 22 C., and the 

 colonies are counted when they have deve- 

 loped. 



(5) Sedgwick and Tucker's method. One of 

 the best and most convenient methods for the 

 bacteriological examination of air. A glass 



tube of special form is employed (Fig. 68) ; p IG> 68. Sedgwick 



this consists of an expanded portion (A) about and Tucker's tube 

 15 cm. long and 4-5 cm. in diameter ; one end of for air analysis, 

 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 sterilised. 

 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 carefully dried and sterilised 

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

 or three hours, the greatest care being taken not to melt the sugar. 



