BREATHING HABITS 157 



grinding or polishing steel or stone, in which dust par- 

 ticles continually fill the air surrounding the workers. 

 Many persons, too careless or too proud to wear such 

 protectors, either have been obliged to give up the 

 dangerous employment or have become the victims of 

 lung disease. Respirators, by keeping out much of 

 the dust, make the employment less harmful. 



