XII. — On Certain Bacteria from the Air of Neiv York City* 



BY HARRISON G. DYAR, A. M. 



Read February IS, 1895. 



It was susjo-ested to me by Dr. T. Mitchell Pruclden that a 

 promising field for research existed in determining the identity of 

 the bacteria commonl}" occurring in the air of Xew York. 



Yer}' early in the investigation a practical difficulty in the way 

 of determining species became apparent. This resulted from the 

 lack of any monographic treatment of the subject from the speci- 

 fic point of view. I find the same difficulty is met with by other 

 investigators. Dr. Paul Schneider begins his inaugural address 

 with these words : " Im Laufe der letzten Jahre sind nach und 

 nach eine solche Menge verschiedener Bakterienarten beschrieben 

 worden, dass es demjenigen, der sich nicht fortwiihrend damit 

 beschaftigt, zur Zeit ganz unmoglich ist, sich in dieser Pflanzen- 

 gruppe, die zwar arm an Formen, aber reich in Arten ist, zurecht 

 zu finden." 



It was thought that this difficulty could be overcome b}' the 

 fjicilities possessed by the bacterial laboratory in the College of 

 Physicians and Surgeons of Columbia College, with its consider- 

 able collection of living species, which might be directly compared 

 with those obtained from the air. Further, a collection of fifty 

 species was ordered from Krai's bacterial laboratorj^ at Prague 

 with this special object in view. It was found, however, that the 

 determinations of the species were not always authentic, as seen 

 b}^ the fact that when planted on the standard media man}- of 

 them contradicted tlieir published characters. The onl}- cultures 

 on which dependence could be placed were a few authentic ones 

 which the college has received, identified by Dr. Sternberg, and 

 those species from the college collection which Dr. Cheesman has 

 had occasion to work out. Therefore, I have had to rely mostly 

 on the published descriptions for identification of my cultures. 



* Submitted in partial fullillraent of the requirements for the degree of 

 Doctor of PhilosojAy, in the University Faculty of Pure Science, Columbia 

 College. 



