92 The Story of the Bacteria 



immediately come in contact with him, but to 

 those who, either where he is, or where he 

 has been, are forced to breathe dust-laden air, 

 the better will it be for all concerned. 



Of course no intelligent person would infer 

 from this statement of facts regarding the 

 sources of infection with tubercle bacilli 

 through the air, that everybody who goes upon 

 the street or enters a hospital or a theatre 

 is going, or is even liable, to acquire tubercu- 

 losis. For, in the first place, the infecting 

 material, even under the worst conditions 

 is enormously diluted by the circulating air 

 and the tubercle bacilli are killed by sunlight, 

 so that the individual chances of coming 

 in contact with the dangerous material are 

 slight. 



In the second place, the average healthy 

 individual is not predisposed to the disease 

 at all, and could be affected only under es- 

 pecially favorable conditions. Third, the 

 amount of infecting material is apt, in trans- 

 mission by the air, to be small, and this is a 

 condition which diminishes the chances of 

 danger from such exposure. 



