Il8 BACTERIOLOGY OF WATER, AIR, MILK, ETC. 



aerobioscope. Now pour in 10 or 15 c.c. of melted gelatin (40 C.) to 

 dissolve sugar. Roll tubes as for Esmarch roll cultures, and incubate 

 at room temperature. To draw air through the aerobioscope, connect 

 the small end with a piece of rubber tubing which is attached to a tube 

 in the stopper of an aspirating bottle. Having poured a definite 

 quantity of w r ater into the aspirating bottle, allow the water to run out. 

 The same quantity of air will be drawn through the sugar of the 

 aerobioscope as the amount of water passing out of the aspirating 

 bottle. The bacteria and moulds are caught by the sugar. 



Example. Passed 10 liters of air through the aerobioscope. The 

 bacteria in this quantity of air showed 75 colonies when incubated 



FIG. 43. Sedgwick-Tucker aerobioscope. (Williams.} 



at 20 C. The unit being one cubic meter or one thousand liters, 

 we have only obtained the bacteria of one hundredth of the unit. 

 Hence multiplying 75 by 100 gives 7,500 bacteria as present in one 

 cubic meter of the air examined. 



In comparing the results with the aerobioscope with those obtained 

 by exposing a plate as in Petri's method for ten instead of five minutes, 

 it was found that the latter was sufficiently in accord to make it a 

 satisfactory approximate quantitative method. The simplicity and 

 ease of access of the colonies developing in it make it preferable when 

 the air of operating-rooms or hospital wards is to be examined. 



