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Cincinnati Society of Natural History. 



been made in different parts of the city itself. A number of 

 exposures have also been obtained in various places in the 

 Territory, and in these instances I have been materially 

 assisted by a number of my students. 



The details of the several experiments will now be recorded 

 and discussed in turn. 



Qualitative Determinations of Air Bacteria. 



Exp. i. — September 28, 1898, 4.00 p. m. Three agar petri 

 plates were exposed 100 feet from University building, to the 

 air for 2, 4, and 6 minutes respectively. 



Conditions : Stiff southwest breeze ; dry ; no rain for 

 several weeks. 



October 3. — Colonies were counted with the following 

 results : 



PL 2 min. — 6 bacteria (3 spp.) and 1 mold. 

 PI. 4 min. — 40 bacteria (4 spp.) and 2 molds. 

 PI. 6 min. — 50 bacteria (4 spp.) and 2 molds. 

 Average per 10 min., 71 bacteria. 



The species of bacteria were A 1; A 2 , A 3 , and A 4 . 

 For descriptions of species, see the end of this paper. The 

 letter "A" was arbitrarily given to all the air bacteria to dis- 

 tinguish them from other cultures in the laboratory. The 

 decided and brilliant colors of these colonies may be of ser- 

 vice to the reader in keeping them in mind. They may be 

 summarized as follows : 



A, — salmon-pink. 



A 2 — sulphur-yellow. 



A : ^ — milky- white. 



A 4 — Orange-yellow. 



A 5 — pink. 



Others — some modification of white. 



Exp. 2. — October 7, 1898, 4.00 p. m. Three agar plates were 

 exposed to air 200 feet east of University building for 2, 4, 

 and 6 minutes respectively. 



Conditions: Gentle breeze blowing; no rain for some 

 weeks; a dozen flies interfered with exposures. 



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