DUST AND ITS DANGERS. 



may be swarming with bacteria does not be- 

 come charged with these. The bacteria, singly 

 or in masses, free, or attached to other par- 

 ticles of one kind or another, must first be 

 dried and then the clusters more or less pul- 

 verized or ground tip, before they are swept 

 away and suspended as a part of the dust in 

 the air. 



There are indeed certain moulds the green 

 mould, for example, which is so common on 

 various moist articles of food which form 

 very light and not easily moistened spores (see 

 Plate I. Fig. i), these may be readily brushed 

 or blown off and mingle with the dust under 

 almost all conditions. 



All sorts of bacteria-laden material then, 

 when dry and ground up as it so readily is 

 by the varied movements of men and animals 

 out-doors and in-doors, may become a part 

 of the floating dust. These dry minute germs, 

 some of which are alive and some dead, com- 

 port themselves in the air just as lifeless dust 

 particles of any other kind do. They are 

 wholly inert, and are driven hither and thither 

 by air currents, now in clouds or masses of al- 



