EXAMINATION OF A1U 731 



(4) Fmnkland's method. The air to be examined is aspirated 

 through a tube 5 in. in length and \ in. in diameter (Fig. 66). 

 One end of the tube is open, the other (c) is plugged with cotton- 

 wool. At a distance of 1 in. from the open end the tube is slightly 

 constricted to support a plug of glass wool (a). At a distance 

 of 2| in. from this plug the tube is again constricted to support 

 a second plug (b), consisting of glass-wool and finely powdered 

 cane-sugar, supported in front arid behind by plugs of glass- waol. 

 Several such tubes having been prepared, they are placed in a tin 

 box and sterilised at 130 C. for three hours, and can then be 

 easily transported without risk of contamination. When required 

 for use, a tube is quickly removed from the box, being handled by 

 the plugged end, which is connected by stout rubber tubing to 

 aspirating 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 



FIG. 66. Frankland's tube for air analysis. 



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 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 labora- 

 tory. 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 plug of glass-wool and sugar is shaken, 

 or pushed by means of 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 dissolves, 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 developed. 



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

 convenient methods for the bacteriological examination of air. 



