BACTERIOLOGY OF AIR 215 



has shown that in the drainage system of an ordinary 

 private house splashing allows the disengagement of 

 bacteria passing down soil-pipes, which bacteria can be 

 carried along a 4-inch drain, against the flow of sewage, 

 for at least 50 feet by ventilation currents. 



Gordon uses the Staphylococcus epidermidis albus as 

 an index of pollution of the air with material detached 

 from the skin. He also detects pollution by material 

 brought in from the street on boots by the presence of 



B. coli, spores of B. Welchii, certain streptococci, and 

 sometimes B. mycoides. 



Gordon uses a streptococcus as an indicator of con- 

 tamination of air with saliva. He found the chief or- 

 ganism present in saliva to be a streptococcus, present to 

 the extent of never less than 10,000,000, and sometimes at 

 least 100,000,000, per cubic centimetre. This strepto- 

 coccus was of the brevis type, growing well anaerobically, 

 and best at 37 C., generally clotting milk with the pro- 

 duction of acidity, and producing acid in glucose, lactose, 

 fructose, maltose, and galactose media. It reduced 

 neutral red much in the same manner as the colon bacillus 

 viz., the cherry-red became changed to a yellowish -green, 

 and was generally non- virulent to mice. Its growth in 

 neutral red broth served as a means for isolating it. The 

 method adopted to examine for contamination with saliva 

 was to use ' broth * plates i.e., a tube of neutral red broth 

 was poured into a Petri dish, exposed to the air, then poured 

 back into the tube, which was incubated anaerobically at 

 37 C. The change in the broth, together with a micro- 

 scopical examination, sufficed to show the presence of the 

 streptococcus. 



Streptococci appear to bulk largely in domestic dust. 



C. A. E. Winslow obtained 22,700 acid-forming streptococci 

 per gramme from an average of nineteen samples of dust 

 taken from New York schoolrooms. 



Filtration of Air. Dry cotton-wool, a dry Pasteur - 

 Chamberland filter, a sufficient number of bends in a 

 narrow tube, or, best of all, glass-wool and sugar, prevent 

 the passage of organisms. 



Examination of Air. For qualitative or comparative 

 examinations, Petri dishes containing a solid medium 

 may be exposed. 



Hesse's apparatus consists essentially of a glass cylinder 



