2Q 2 DISTRIBUTION OF BACTERIA 



the lead of Ravenel, has shown that the distribution of tuber- 

 culosis may be accounted for in other ways, to a certain extent 

 at least. Bact. diphtheriae may be distributed through the air, 

 and this germ can undoubtedly live for long periods of time in 

 the air. Other diseases that were formerly supposed to be air- 

 borne, such as influenza, are now accounted for, so far as their 

 distribution is concerned, in other ways. In a considerable 

 number of other diseases, such as the acute exanthemata, 

 which includes smallpox, measles, and scarlet fever, evi- 

 dence seems to point to the air as a vehicle of transmission. 

 It should be noted that in the past it has been largely true 

 that we have attributed to the air an important role when we 

 have been largely or completely ignorant of the cause and 

 means of distribution of these diseases. As our knowledge 

 has become more exact, we have found that the air has had less 

 to do with it than was formerly supposed. Whether this is 

 generally true or not only time can tell. But we do not have 

 at the present time any convincing evidence that any disease 

 is either in whole or in part largely spread through the air. 

 Of the saprophytes which persist in the air for long periods of 

 time and constitute very largely the bacterial flora of the air, 

 the micrococci are the most prominent. Among these are 

 many brilliant chromogenic forms. In addition to bacteria 

 there is always present a considerable number of mold spores 

 and yeast cells. 



