216 



Cincinnati Society of Natural History. 



Exp. 5. — October 20, 1898. Three plates were exposed 500 

 feet from main building for 2, 4, and 6 minutes respectively. 

 A moderate breeze was blowing from the west, i. <?., from the 

 city toward the University grounds. 



October 27 : 



PI. 2 min. — (agar), 10 bacteria. 



PI. 4 min. — (gelatin), spoiled. 



PI. 6 min. — (agar), 30 bacteria. 



Average per 10 min., 50 bacteria. 

 Spp. : A 1} A,, A 3) A,, and A 9 . 



Exp. 6. — November 17, 1898, 10.00 A. m. Made three agar 

 plate exposures 15 rods northeast of main building for 4, 6, 

 and 12 minutes. Air was clear, calm, and warm. No rain for 

 some time. 



November 22 : 



PI. 4 min. — 2 bacteria and 1 mold. 

 PI. 6 min. — 5 bacteria and 1 mold. 

 PI. 12 min. — 5 bacteria and 1 mold. 

 Average per 10 min., 5.8 bacteria. 

 Beside other colonies, A 6 and A 7 were isolated. The great 

 relative falling off in number, even with increased time, is 

 remarkable. 



Exp. 7. — November 28, 1898, 10.00 a. m. Made three plate 

 exposures about 500 feet north of buildings. 



Conditions : Clear and cold with moderate south breeze. 

 Five inches of snow fell on the 26th and nearly disappeared 

 on the following day. 



December 12 : 



PL 5 min. — (agar), 4 bacteria and 1 mold. 

 PI. 10 min. — (agar), 26 bacteria and 2 molds. 

 PI. 10 min. — (gelatin), 1 bacteria and o mold. 

 Average per 10 min., 11.6 bacteria. 

 This experiment illustrates the weakness of our method of 

 analysis. The variation in the number of bacteria that fell 

 upon the several plates is most remarkable. This is not 

 wholly a disadvantage, however, for it shows the decided 

 irregularity existing in the number of bacteria that different 

 portions of the air may contain at the same time. This 



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