n8 LABORATORY GUIDE IN BACTERIOLOGY 

 EXERCISE II. BACTERIOLOGICAL EXAMINATION OF AIR 



An approximate determination of the number of 

 bacteria in the air can be made by the following simple 

 method: Place a certain amount (50 c.c.) of broth in 

 an Erlenmeyer flask (Fig. 36, a). This flask is provided 

 with a rubber stopper (b), provided with two holes, 

 through which the two glass tubes (c with a wide opening 



FIG. 36 

 Apparatus for Determining the Number of Bacteria in a Definite 



a. Erlenmeyer flask 



b. Rubber stopper 

 c-d. Glass tubes 



Volume of Air 



/. Five-liter flask 

 g-h. Glass tubes 

 *. Pinchcock 



and d) lead. Cotton plugs are then inserted at c and d, 

 and the apparatus is sterilized in the autoclav. A 

 large bottle (/), containing 5 liters of water, is then 

 provided with a rubber stopper, and also with two glass 

 tubes (g and h)\ h is connected with a short piece of 

 rubber hose and a pinchcock (i). When the Erlen- 



