604 A MANUAL OF BACTERIOLOGY 



medium by a strong current of air. The medium on 

 which they are growing must dry up completely and crumble 

 into fine dust before they can be distributed through the 

 agency of air-currents (but see p. 365). 



The number of organisms in the air varies with the 

 season, with rain, with altitude, with movement, etc. At 

 Montsouris, Miquel found in one cubic metre of air 49 

 organisms in winter, 85 in spring, 105 in summer, and 

 142 in autumn. After heavy rain the air is largely freed 

 from organisms. Frankland found at Norwich Cathedral 

 at an altitude of 300 feet 7 organisms in two gallons, while 

 on the ground 18 were found ; at the Golden Gallery at 

 St. Paul's two gallons of air contained 11 organisms ; in 

 St. Paul's churchyard the number was 70. On high 

 mountains organisms are nearly absent from the air, and 

 the same is the case at sea at a distance from land exceeding 

 about 100 miles. Organisms are much fewer in the air 

 of the country than in that of towns. At the entrance-hall, 

 Natural History Museum, South Kensington, Frankland 

 found in the morning 30 organisms ; in the afternoon, 

 when many visitors were present, the number had risen 

 to 292, showing the influence of movement. By keeping a 

 volume of air absolutely still, enclosed in a box the walls 

 of which were smeared with glycerin, Tyndall was able 

 to free it completely from particles and organisms. The 

 writer found from 43 to 150 organisms per 10 litres of air 

 in some of the principal streets of London during the 

 daytime. 



Gordon, 1 by exposing dishes of neutral-red broth to the 

 air, or by aspirating air through neutral-red broth (p. 591) 

 has been able to detect the presence of the S. salivarius, 

 M. epidermidis, and scurf micrococcus (p. 230) in air 

 subjected to human contamination. By these tests and 

 by the use of B. prodigiosus as an indicator he concludes 

 1 Reps. Med. Off. Loc. Gov. Board for 1902-1904. 



