Hazards of the Air 201 



phagocytes take it up as fast as they can and 

 carry it along the lymph channels. Some 

 of it is left in little cell masses called lymph 

 nodules which are placed along the course of 

 these channels. Some is carried along to the 

 clusters of lymph-nodes at the base of the 

 lungs. These lymph nodules and lymph- 

 nodes are thus places of deposit for foreign 

 things gathered by phagocytes. In these, too, 

 as we have seen, the phagocytes complete their 

 destruction of bacteria and various tissue 

 fragments which they have gathered. 



Now if these important way stations and 

 places of final disposal become blocked up by 

 excessive amounts of dust brought to them, 

 the body is deprived of one of its important 

 safeguards against infection. 



How much of this sooty dust people 

 sometimes accumulate in their lungs is seen 

 in Plate XII. This figure is a copy of a 

 photograph of a lung of a resident of a large 

 city, who had spent several hours each day, 

 for years, in public assembly places. The 

 amount of black dust is deposited over the 

 surface of the lung in the lymph nodules 



