DUST AND ITS DANGERS. 5 



or woollen-dust or tobacco-dust, etc., are apt to 

 become victims of more or less well marked 

 pulmonary affections, which are to be found 

 fully described in systematic treatises among 

 the so-called " diseases of occupation." 



It is not with these exceptional places nor 

 with the special conditions which belong to 

 them that we are now concerned, but with the 

 conditions under which both well and sick peo- 

 ple of all classes are placed, especially in cities, 

 and more particularly when in-doors. Nor 

 shall we occupy ourselves here to any consid- 

 erable extent with the inorganic ingredients of 

 dust, but more especially with those living 

 components called micro-organisms, be they 

 either bacteria or moulds. 



I purpose, in the first place, drawing upon 

 the results of various old and recent studies, to 

 indicate the sources of the living germs which 

 form such an important part of the dust of in- 

 habited regions, the ways in which they get 

 disseminated in the air, and their general de- 

 portment as they are driven hither and thither 

 by the winds, sway poised in the still air of quiet 

 places, or settle slowly to the ground. 



