DUST AND ITS DANGERS. 



Now a good many plans have been devised 



for finding out how many living germs are 



present in a given volume of dusty air. We 



A 



FIG. I. 



Fig. i. A A single "colony" of rod-shaped bacteria (Bacilli) 

 growing on a plate of nutrient gelatine. The actual diameter of this 

 colony was about one-fourth of an inch. B A cluster of the bacilli 

 taken from the colony and highly magnified. 



may force a given volume of the air through a 

 tube which has been plugged with cotton-bat- 

 ting previously heated so hot as to kill any 



