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passages into the air during coughing, sneezing and loud speak- 

 ing, and that the bacteria so expelled are wafted by air currents, 

 such as exist in ordinary rooms, to distances as far away as 

 40 feet. These facts were demonstrated by artificially infecting 

 the mouth with B. prodigiosus and then performing the above- 

 mentioned acts. 



While the bacilli extruded into the air by these agencies are 

 numerous they settle rapidly. Koeniger, for example, found 

 that 60 per cent, of the bacteria sprayed out in this way dis- 

 appeared from the air in ten minutes, while after twenty minutes 

 less than 10 per cent, of the original number remained. Winslow 

 and Robinson 1 have recently obtained very similar results, and 

 they remark, " Clearly the mouth spray is a fairly coarse rain 

 which settles out for the most part in 15 or 20 minutes." 



Winslow and Robinson found that after inoculating the 

 mouth with a rich culture of B. prodigiosus and speaking loudly 

 and with vigorous enunciation for 15 minutes only seven colonies 

 of the specific germ could be obtained from 140 litres of air 

 collected at the close of the speaking from various points in 

 front of the speaker. 



In a number of cases persons suffering from pulmonary 

 tuberculosis have been experimented with and B. tuberculosis 

 expelled by them in the act of coughing demonstrated to pene- 

 trate through the air to a distance of about one metre from the 

 mouth of the patient. Heymann (1899) succeeded in infecting 

 six out of 25 guinea-pigs exposed 20 to 45 cm. in front of 

 coughing consumptives. 



Gordon 2 has greatly extended our knowledge of such par- 

 ticulate pollution, and has shown that certain bacteria, which 

 can be detected and estimated, furnish means whereby these 

 different kinds of pollution can be recognized. 



He has shown that certain streptococci are present in 

 enormous numbers in human saliva, and that their presence 

 serves as a means whereby the addition of saliva to air can be 

 detected. 



Using salivary streptococci as the test he confirmed Fliigge's 



1 fourn. of Inf. Diseases^ 1910, vol. VII, p. 17. 



2 Local Government Board Medical Officers Report, 1902-3, p. 42?. 



S. W. 10 



