226 



Cincinnati Society of Natural History. 



Fig. hi. 



Plate B, exposed to air for four minutes in business district 

 of Albuquerque, at 6.00 p. M. 



Fig. IV. 



Plate D, exposed to air for four minutes in business district 

 of Albuquerque, at 8.30 A. M. 

 These figures present a striking illustration of the relative numbers of bac- 

 teria contained in the air at the closing and opening of business. 



16 



