July 15, 1915 



Methods of Bacterial Analyses of Air 



347 



The counting of the colonies on the plates was done with the aid of 

 a hand lens. The term "bacteria" used throughout this paper includes 

 yeasts and actinomycetes, since no attempt was made to separate these 

 from the bacteria proper. IMolds were noted and recorded separately, 

 but are not given here. In general they were abundant 

 and at times more numerous than the bacteria. 





\ 



Fig. I.— Standard 

 aeroscope. 



DESCRIPTION OF AEROSCOPES 



The term "aeroscope," as used in this paper, indicates 

 an apparatus used to gather bacteria from the air. It does 

 not include the accessories, such as the aspirator bottle and 

 its connections. In the past there has been some varia- 

 tion in the use of the term among different writers. 

 Usually where the principle of filtration through sand was 

 employed, the apparatus has not been called an "aero- 

 scope," while the term is almost always applied to an 

 apparatus in which a liquid is used as the filtering agent. 

 There seems no good reason for this dis- 

 tinction. Likewise there seems to be very 

 little justification for restricting the word 

 to a part of the apparatus, as is done by 

 Rettger (22). 



The aeroscope referred to in this paper 

 (fig. i) as the "standard" is constructed as 

 follows: A lo-mm. layer of sand which has been passed 

 through a loo-mesh sieve and has been retained by a 

 200-mesh sieve is supported within a cylindrical glass 

 tube 70 mm. in length and 15 mm. in diameter upon a 

 layer of bolting cloth folded over the end of a rubber 

 stopper. Through a perforation in the stopper there 

 passes a tube 6 mm. in diameter and 40 mm. in length. 

 This tube is attached to the aspirator bottle. The upper 

 end of the cylindrical tube is closed by a perforated rub- 

 ber stopper through which is passed a glass tube 40 mm. 

 in length and 6 mm. in diameter bent at an angle of 45° 

 in order to prevent precipitation of bacteria or dust parti- 

 cles into the aeroscope. 



In using this aeroscope a measured volume of air is 



filtered through the tube, the sand shaken out into 10 c. c. 



of sterile water, and aliquot portions of this suspension 



plated on nutrient agar. 



The "modified" form (fig. 2) of the standard aeroscope (fig. i) differs 



from the standard in that the lower rubber-stopper and bolting-cloth 



supports are eliminated and the small tube is fused into the larger one. 



The layer of sand is supported by a layer of cotton resting on the shoulder 



Fig. 2. — Modified 

 standard aero- 

 scope. 



