DUST AND ITS DANGERS. 95 



much more readily transmitted than is diph- 

 theria or consumption ; they are, as we say, 

 more highly contagious, and although we do 

 not yet exactly know what form of germ causes 

 scarlet-fever and measles and small-pox, we are 

 pretty certain that they are caused by germs 

 or lowly organisms of some kind, and that 

 these are much more readily or freely given 

 off from the body than are the germs which 

 cause less easily communicated diseases, such 

 as consumption and diphtheria, and are more 

 liable to exist in the form of particles which 

 float in the air as impalpable dust. 



Then, again, we should not lose sight of the 

 fact that the germ of consumption is a very 

 slowly-growing germ ; that only under a very 

 limited range of conditions does it grow at all, 

 and that after all the chances are not very 

 great for each one of us that from aerial con- 

 taminations a sufficient number of the living 

 bacilli, even if breathed in and passing all the 

 safeguards of the body against such intruders, 

 at last find lodgment in the tissues, will find the 

 conditions favorable for a sufficient growth to 

 induce the disease. Now and again only does 



