THE MICROORGANISMS OF THF AIR 



307 



authors are appended to serve as an index to what may be expected in 

 the air content of bacteria. 



SPECIES OF ORGANISMS IN THE AIR. Penicillium is the most com- 

 mon mold isolated from the air. Next in importance are Mucor, 

 Rhizopus, and Aspergillus in the order given. In addition to these a 

 considerable number of species of hyphomycetous molds are occasion- 

 ally found. Torula, but not true yeasts, are usually common. Bac- 

 teria are either spore-bearing soil bacilli or cocci. Of the former, B. sub- 

 tilis, B. mycoides, and related forms are ubiquitous. Sarcina lutea and 

 Sarcina aurantiaca and certain other chromogenic cocci are to be found 

 in almost every plate exposed. Since the air does not have a true flora, 

 the species as well as the number of bacteria present must depend en- 

 tirely upon the character of the environment. 



