146 AIR 



results and showed the presence of particles of saliva in air at a 

 distance of 40 feet in front of the speaker and even at a distance 

 of 12 feet behind him. 



To render this test reliable it must be shown that these 

 streptococci are not usually present in air. Gordon has care- 

 fully examined the open air of London, E.G., and at Black- 

 heath, S.E. He carried out ten observations upon London E.G. 

 air, 50 litres being examined for each experiment. Streptococci 

 were obtained from the air on eight of these ten occasions but 

 only one of these appeared to be the Streptococcus salivarius of 

 saliva. With Blackheath air streptococci were obtained on only 

 three occasions, while in each of these experiments as much as 

 100 litres of air were examined. All three were air streptococci. 



His results showed that while streptococci were readily 

 found in rooms used for speaking and working they were very 

 rare in open air and that when present the varieties were almost 

 invariably strains not ordinarily met with in saliva. 



According to Gordon, pollution of three separate kinds can 

 be recognized by bacterial tests. 



a. Pollution from Material derived from the Upper Respira- 

 tory Passages. The organism specially characteristic of such 

 pollution is the Streptococcus salivarius. 



The method advocated to detect it is to expose Petri-dishes 

 containing broth to the air. The broth is then incubated ana- 

 erobically for forty-eight hours at 37 C. By brushing over agar 

 plates the streptococci are isolated in pure culture, and their 

 morphological and biological properties determined. Instead 

 of broth, ordinary agar plates may be employed. 



b. Pollution from Material detached from the Skin. Gordon 

 has shown 1 that the Staphylococcus epidermidis albus is con- 

 stantly present on the human skin, and that by its detection in 

 air the presence of particles detached from the skin may be 

 deduced. It may be detected by the same methods as for the 

 Streptococcus salivarius. 



c. Pollution by Material brought in from the street on 

 boots. Such material consists largely of horse-dung, and may 



1 ibid. 1904-5, p. 387. 



