658 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
of molds found was 1,100 per cubic meter. This observation was 
made in the tunnel under Central Park. 
The average ratio of molds to bacteria, as determined by the obser- 
vations with filters, was 1 to 40 in the subway. . 
The wind in the streets had a decided effect upon the numbers of 
bacteria collected from the air, both inside and outside of the sub- 
way. ‘The averages show that five times as many were recoverable 
from the air in the streets with a wind of 18 miles per hour as with a 
wind of 9 miles. 
No attempt was made to identify the different kinds of bacteria. 
To have undertaken to name the species, even with a great deal more 
time than was available and a special corps of bacteriologists, would 
probably have produced little result. Nevertheless, the conclusion 
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Fic. 8.—Average numbers of bacteria which subsided from the air per square foot per 
minute, as determined by the plate method, in the subway and streets from July 10 to 
October 2, 1905. The number of samples represented is 2,742. 
was reached that most of the bacteria in the subway come from the 
streets. The principal reasons for holding this view follow: 
1. The numbers of bacteria recovered from the air of the subway 
varied with the more decided changes in the streets. 
2. The bacteria were more numerous at the subway stations near 
the stairways than at the remote ends of the platforms. 
3. In the subway stations, the bacteria were more numerous on that 
side of the road toward which the wind blew than on the opposite 
side. 
4. There were more bacteria at the arrival ends of the platforms of 
the stations than at the departure ends. 
5. Street dirt, probably containing large numbers of bacteria, was 
often carried down the stairways into the subway by inrushing cur- 
rents of air and by the passengers. 
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