608 BACTERIOLOGY. 



pump one exhausts the cylinder until the needle 

 reaches the mark corresponding to the amount of air 

 required.' 



A sterilized aerobioscope is now to be fixed in the 

 upright position and its small end connected by a rubber 

 tube with a stopcock on the cylinder, or to a glass tube 

 tightly fixed in the neck of an aspirating-bottle by 

 means of a perforated rubber stopper. The cotton plug 

 is then moved from the upper end of the aerobioscope, 

 and the desired amount of air is aspirated through the 

 sugar. Dust-particles and bacteria will be held back 

 by the sugar. During manipulation the cotton plug is 

 to be protected from contamination. 



When the required amount of air has been aspirated 

 through the sugar the cotton plug is replaced, and by 

 gently tapping the aerobioscope while held in an almost 

 horizontal position the sugar, and with it the bacteria, 

 are brought into the large part (e) of the apparatus. 

 When all the sugar is thus shaken down into this part 

 of the apparatus about 20 c.c. of liquefied, sterilized 

 gelatin is poured in through the opening at the end c, 

 the sugar dissolves, and the whole is then rolled on ice, 

 just as is done in the preparation of an ordinary Esmarch 

 tube. 



The gelatin is most easily poured into the aerobio- 

 scope by the use of a small, sterilized, cylindrical funnel 

 (Fig. 110), the stem of which is bent to an angle of 

 about 110° with the long axis of the body. 



1 Sacli a cylinder and air-pump are not necessary. A pair of ordinary 

 aspirating-bottles of known capacity graduated into litres and fractions 

 thereof answer perfectly well. Or one can determine by the weight 

 of water that has flowed from the aspirator the volume of air that has 

 passed in to take its place — i. e., the volume of air that has passed 

 through the aerobioscope. 



