IOWA ACADEMY OP SCIENCES 
23 
floor is moist, then the bacteria will adhere. So long as the dust and 
bacteria are moist they will not be taken up to any very great extent 
from the surface by ordinary air currents. It has been known for a 
number of years that the air in sewers is much more nearly pure bacter- 
iologically than is the air of the street. It is not necessary to state that 
in order to keep the air of the school room as nearly free from bacteria as 
possible, the floor, the walls, and furniture must be kept as thoroughly 
cleansed from dust as practicable. 
I 
