DUST AND ITS DANGERS. 51 



which dust particles of one kind or another 

 may do serious harm to human beings. 



We shall do well in considering these 

 harmful effects of dust to separate in our 

 thought its inorganic from its germ ingredi- 

 ents. 



The inorganic elements of dust when present 

 in large quantities in the inhaled air may, as 

 we have seen above, cause well-defined disease 

 of the lungs by the persistent irritation which 

 they induce. But as it is only under excep- 

 tional conditions, as among coal-miners and 

 grinders and other workers in confined places 

 where these solid particles are set free in great 

 numbers that this occurs, we need not con- 

 sider them here. Very moderate amounts 

 of dust particles in sensitive persons cause 

 such a degree of irritation of the respiratory 

 organs as either to deprive them of robust 

 health or predispose them to the aquirement 

 of various diseases which with unirritated 

 lungs they would readily resist. 



There is no doubt that a great deal of 

 misery, if not positive disease, is caused by the 

 inhalation of dust in the persistent coughs and 



