MICROBIAL AIR INFLUENCE IN FERMENTATION, DISEASES, ETC. 253 



fore conclude that air is of secondary importance as a carrier of infection. 

 It may be of importance in a crowded workroom, but even under these 

 conditions it is probable that transmission of infection comes about 

 more frequently through actual contact or through food and drink. 



Organisms of the Air and Fermentations. — A uniform inocula- 

 tion with soil bacteria such as produce the nodules on the roots of leg- 

 umes is obtained over considerable areas through the action of the wind 

 in blowing dust particles. The bacterial flora of milk is to some extent 

 dependent upon air currents as is also the development of the molds 

 mecessary to the proper ripening of cheese, such as the Camembert. 

 Acetic, butyric, and other organisms are likewise distributed in this 

 manner. The organisms responsible for putrefaction and decay, the 

 molding and spoiling of foods are wind-borne. 



Freeing Air from Bacteria. — Air is most commonly freed from 

 bacteria by sedimentation, for this is the ultimate fate of most dust par- 

 ticles. We have seen that they gradually subside in a quiet atmos- 

 phere. When large quantities of pure air are required, dust and bac- 

 teria may be removed by passage through a spray of water or through 

 various types of filters, such as cotton, glass, wool, etc. A familiar 

 example of this tj^e of filtration is the laboratory use of cotton plugs in 

 test-tubes. It is sometimes necessary to resort to fumigation to destroy 

 the organisms of the air when an undesirable species ^s present. 



