DUST AND ITS DANGERS. 97 



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 slowly, 

 growing germ ; that it is killed by sunlight ; 

 that only under a 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 contaminations 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 

 inducing the disease. Now and again only does 



