136 BACTERIOLOGY OF WATER, AIR, MILK, ETC. 



(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 aspirat- 

 ing bottle. Having poured a definite quantity of water 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 ten liters of air through the aerobioscope. The bacteria in 

 this quantity of air showed 75 colonies when incubated 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 7500 bacteria as present 

 in one cubic meter of the air examined. 



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



In comparing the results with the aerobiscope 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 satis- 

 factory approximate quantitative method. The simplicity and ease of 

 access to the colonies developing on it make it preferable when the air of 

 operating-rooms or hospital wards is to be examined. 



Of the fungi ordinarily obtained in examinations of the air the blue-green mould 

 and the red yeast are the most common. B. subtilis and sarcina types of cocci are 

 the most common bacterial colonies found upon exposed plates. Sewer air is as a 

 rule free from bacteria, due probably to the fact that bacteria tend to adhere to 

 moist surfaces.' The importance of Fliigge's droplet method of contamination of 

 the air of a room is brought out in the discussion of infection with pneumonic plague. 

 This is an important method in the transmission of tuberculosis. 



