188 BACTERIOLOGY. 



(2) A stout copper cylinder of about sixteen litres 

 capacity, provided with a vacuum-gauge. 



(3) An air-pump. 



The aerobioscope (Fig. 31) is about 35 cm. in its en- 

 tire length ; it is 15 cm. long and 4.5 cm. in diameter at 

 its expanded part ; one end of the expanded part is nar- 

 rowed down to a neck 2.5 cm. in diameter and 2.5 cm. 

 long. To the other end is fused a glass tube 15 cm. 

 long and 0.5 cm. inside diameter, in which is to be 

 placed the filtering material. 



FIG. 31. 



Upon this narrow tube, 5 cm. from the lower end, a 

 mark is made with a file, and up to this mark a small 

 roll of brass-wire gauze (a) is inserted ; this serves as a 

 stop for the filtering material which is to be placed over 

 it. Beneath the gauze at (6), and also at the large end 

 (c), the apparatus is plugged with cotton. When thor- 

 oughly cleaned, dried, and plugged, the apparatus is to 

 be sterilized in the hot-air sterilizer. When cool, the 

 cotton plug is removed from the large end (c), and 

 sterilized No. 50 granulated sugar is poured in until 

 it just fills the 10 cm. (d) of the narrow tube above 

 the wire gauze. This column of sugar is the filtering 

 material employed to engage and retain the microorgan- 

 isms. After pouring in the sugar, the cotton-wool plug 

 is replaced, and the tube is again sterilized at 120 C. 

 for several hours. 



