2 go DISTRIBUTION OF BACTERIA 



largely from the soil layers beneath. A great many different 

 kinds of bacteria find their way into the air, but a great many 

 of them are unable to withstand the desiccation to which they 

 are subjected, so that certain forms die off and others remain. 

 Thus there is established a more or less characteristic bacterio- 

 logical flora. The extreme minuteness of the bacteria permits 

 them to remain in the air for long periods of time. 



Bacteria cannot be dislodged from a moist surface. They 



^ 

 would not be blown into the air, for instance, from the surface 



of water. The only way that water bacteria can get into the 

 air would be to have them shot into it by the bursting of 

 bubbles of gas. This question is one of considerable practical 

 importance, due to the discussion which has frequently occurred 

 in regard to the bacteria in sewer air. The air from sewers 

 is usually low in its germ content, due to the fact that the 

 sewage, and the walls of the sewers, are moist. These consid- 

 erations, as well as those discussed elsewhere, lead to the 

 belief that sewer air is not as great a factor in the produc- 

 tion of disease as was formerly supposed. It is quite likely 

 that in cases where it was supposed to be the cause of disease 

 it was merely a concomitant circumstance. Furthermore, 

 the bacteria of disease are not likely to occur in the breath 

 of those suffering from disease for the same reason. They are 

 very frequently shot from the mouth of diseased persons during 

 fits of coughing and sneezing, and, to lesser extent, during talk- 

 ing, in little droplets of sputum. When these " droplets " dry, 

 then the bacteria in them may get into the air. 



