THE DUST WE HAVE TO BREATHE. 291 



are as nothing compared with the mischief it is calcu- 

 lated to produce in a more subtle manner. In every 

 specimen examined by Mr. Dancer, animal life was 

 abundant. But the amount of " molecular activity " 

 such is the euphuism under which what is exceedingly 

 disagreeable to contemplate is spoken about is vari- 

 able according to the height at which the dust is 

 collected. And of all heights which these molecular 

 wretches could select for the display of their activity, 

 the'height of five feet is that which lias been found to 

 be the favorite. Just at the average height of the 

 foot-passenger's mouth these moving organisms are 

 always waiting to be devoured and to make us ill. 

 And this is not all. As if animal abominations were 

 insufficient, a large proportion of vegetable matter 

 also disports itself in the light dust of our streets. 

 The observations show that in thoroughfares where 

 there are many animals engaged in the traffic, the 

 greater part of the vegetable matter thus floating about 

 " consists of what has passed through the stomachs of 

 animals," or has suffered decomposition in some way 

 or other. This unpleasing matter, like the " molecular 

 uctivity," floats about at a height of five feet, or there- 

 abouts. 



After this, one begins to recognize the manner in 

 which some diseases propagate themselves. "What had 

 been mysterious in the history of plagues a,nd pesti- 

 lences seems to receive at least a partial solution. 



