BACTERIOLOGICAL ANALYSIS OF AIR 629 



ized in the hot-air steriHzer. When cool the cotton plug is 

 removed from the large end (c), and thoroughly dried 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 bacteria. After pouring in the sugar 

 the cotton-wool plug is replaced, and the tube is again 

 sterilized at 120° C. for several hoiu-s. 



Taking the air sample. In order to measure the amount 

 of air used the value of each degree on the vacuum-gauge 

 is determined in terms of air by means of an air-meter, or 

 by calculation from the known capacity of the cylinder. 



Fig. 112 



The Sedgwick-Tucker aerobioscope. 



This fact ascertained, the negative pressure indicated by 

 the needle on exhausting the cylinder shows the volume of 

 air which must pass into it in order to fill the vacuum. By 

 means of the air-pump one exhausts the cylinder until the 

 needle reaches the mark corresponding to the amount of 

 air required. 1 



A sterilized aerobioscope is now to be fixed in the upright 

 position and its small end connected by a rubber tube 



^Such 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. 



