The Mickoscope. 103 



these cases for tubercle bacilli, showed them to be absent in all 

 cases except the first, but in each specimen those round cells 

 were present in increased number and containing in the case of 

 patient II., bits of coal and coal pigment. In some specimens, 

 the crystalline character of the pieces of coal could be lecognized 

 within the cell wall, but more usually the cells were dotted with 

 black points. Of course this has been observed before in patients 

 under similar circumstances, and also in the morning sputum of 

 smokers, but the whole subject seems interesting when the func- 

 tion of these cells is considered. 



To take a hasty view of our manner of breathing, it can be 

 easily seen that man being upriglit and far from the ground is 

 not so apt to inhale certain kinds of dust as grazing animals, 

 hence his nasal passages are more simply constructed. They 

 are moist, and this moisture undoubtely stops the entrance of 

 dust ; the secretion is slightly acid, which may act fatally on 

 invading bacteria. Then dust ;ind foreign particles have to con- 

 tend against a sensitive larynx which may cough them out, and 

 a very active ciliated membrane which is constantly carrying on 

 its waving motion from the small bronchi up towards the larynx, 

 and must drive out dust which gets thus far. Now the role of 

 these cells, which are evidently carrier cells, scavenger cells, 

 wandering cells or phagocytes, is to seize such particles which 

 penetrate to the alveoli of the lungs, carry them off or render 

 them harmless. It is easy to see that the ciliated epithelium 

 can much more easily carry off a round or oval cell which is 

 easily moved, than it can take away very small bits of dust, often 

 angular. In the cases mentioned, the phagocytes are disposing 

 of these foreign substances either by helping them out of the 

 lungs through the trachea in the expectoration, or in cases where 

 the angular pieces of coal or slate dust make their way through 

 or between the alveoli into the lung tissue, the phagocytes carry 

 them by the lymph channels to the nearest lymphatic gland, 

 where they are at least harmless. In- Case II., it is interesting to 

 note the activity of the phagocytes still attempting to carry off 

 what dust they can find, although it is a year since the man gave 

 up his occupation. In such cases as those cited, a post-mortem 

 examination of the bronchial glands shows them to be absolutely 

 black, grey, etc., according to the character of the dust inhaled. 

 Indeed all citv dwellers have to a certain extent these dark 



