BACTERIOLOGIC EXAMINATION OF AIR 177 



shown in Fig. 105. The rubber cap is then removed from the end of 

 the horizontal tube and enough suction by mouth made at the exit 

 tube of the lower and empty flask to start the water running from 

 the upper flask. The water then siphons out of the higher flask into 

 the lower one, and during this process two liters of air are aspirated 

 through the gelatin coated tube. The outer end of the tube is then 

 closed with the rubber cap and the suction flasks reversed. The cap 

 is again removed, and as suction is made on the empty flask the water 

 flows as before from the upper to the lower flask and two more liters 

 of air are aspirated through the gelatin-coated tube. The operation 

 is repeated a number of times until about 20 liters of air have been 



FIG. 105 



Hesse's apparatus for collecting bacteria from the air. (McFarland.) 



aspirated The long tube is then disconnected, closed at both ends 

 with sterile cotton plugs, and kept in a horizontal position for several 

 days to permit the colonies to develop. These are then counted. 

 During the aspiration the water should flow at such a rate that 1 liter 

 passes from the upper to the lower flask in one to two minutes. 



EYRE'S METHOD. Eyre recommends the following apparatus and 

 method of quantitative bacteriologic examination of air: 



Apparatus. 1. Aspirator bottle, 10 liters' capacity, fitted with a 

 delivery tube, and having its mouth closed with a perforated rubber 

 stopper, through which a short length of glass tubing passes. 



2. Erlenmeyer flask, 250 c.c. capacity (having a wide mouth, 

 properly plugged with cotton), containing 50 c.c. sterile bouillon. 

 12 



