54 DUST AND ITS DANGERS. 



man in this region, we find that they are the 

 bodies of persons, and occasionally animals, 

 suffering from the diseases which the bacteria 

 cause. It is the presence of these bacteria in 

 large numbers given off from the body, which 

 makes these diseases what we call infectious 

 or communicable. 



If we could completely isolate all those per- 

 sons or animals who are at the present moment 

 harboring the few known species of bacteria 

 which produce disease in man, such diseases 

 could be largely stricken from the list of 

 human ills. U nless they were lighted up afresh 

 by some of the discharged material which on 

 walls, or garments, or in the soil, or in the 

 aerial dust, still retained vitality. At any rate, 

 if we could be certain that the discharged 

 material from such sick people were immedi- 

 ately destroyed we should be able to limit 

 within narrow bounds those diseases which to- 

 day carry off, prematurely, the larger part of 

 those who do not die of injuries or of old age. 

 They are thus, at least ideally, preventible 

 diseases. 



But this matter of preventing the spread of 



