RESPIRATION 323 



investigation has shown clearly that it is to dust inhalation that 

 this excess is solely due. 15 



A very large proportion of the dust in inspired air is caught on 

 the sides of the nasal and bronchial inspiratory passages, from 

 which it is continuously removed by the action of the ciliated 

 epithelium. It is only the very finest particles that penetrate to the 

 lung alveoli. Nevertheless large amounts of dust do, as a matter 



of fact, reach the alveoli. Arnold showed that even what, in human 

 experience, is relatively harmless dust, will produce, if inhaled 

 in very large amount, foci of scattered broncho-pneumonia in the 

 lungs, and that quartz dust is specially apt to produce inflam- 

 matory changes followed by development of connective tissue. 18 

 In connection with the use of shale dust for preventing colliery 

 explosions Beattie showed that neither coal dust nor shale dust 

 produce any harm in animals if the dust is inhaled in the moder- 

 ate quantities comparable to what a miner inhales. On the other 

 hand, the dust from grindstones produces signs of fibrosis. 17 The 

 subject was followed further in my laboratory by Mavrogardato 

 in an investigation undertaken for the Medical Research Com- 

 mittee. 18 This work showed that the very fine particles which 

 reach the alveoli are rapidly taken up by special cells of the al- 

 veolar walls. When coal dust or shale dust was inhaled, these cells 

 soon detached themselves and wandered away with their load of 

 dust particles. Some pass directly into the open ends of the bron- 

 chial tubes, and are thence swept upwards by the cilia. Others 

 pass into lymphatic vessels and are carried to the nodules of lym- 



15 Haldane, Martin, and Thomas, Report on the Health of Cornish Miners, 

 Parl. Paper Cd, 2091, 1904. 



18 Arnold, Untersuchungen uber Staubinhalation und Staubmetastase, 1885. 



17 Beattie, First Report of Explosions in Mines Committee, Parl. Paper, Cd, 

 6307. 1912. 



18 Mavrogardato, Journ. of Hygiene, XVII, p. 439, 1918. 



