DUST AND ITS DANGERS. 41 



foreign bodies which are breathed into the 

 lungs. There are certain cells in the body 

 which seem to have nothing in particular to do 

 on ordinary occasions but to float about on the 

 blood tides or wander through the various 

 channels and crevices of the tissues watching 

 other cells work. Sometimes they come out 

 and air themselves in the bronchial tubes or in 

 the tiny air-chambers which make up the body 

 of the lungs. But the moment these cells 

 come upon a foreign particle from without or 

 upon a fragment of worn-out tissue anywhere 

 in the body they pounce upon it, wrap them- 

 selves around it, and either digest or destroy 

 it or carry it off to some safe place of deposit, 

 either inside the tissues or without. Now these 

 humble scavenger cells are usually quite abun- 

 dant in the air passages, where they often take 

 up dust particles of one kind or another, and 

 victims to their zeal are not infrequently swept 

 with their booty by the ciliated cells up and 

 away into the mouth. A good deal of lore has 

 accumulated about these little wandering scav- 

 engers of the body and they seem to be of great 

 importance in many ways. But, in spite of 



