ATR OF NEW YORK SUBWAY—SOPER. 657 
diameter, containing a standard agar culture medium (see fig. 7) 
and by collecting them from the air by means of sand filters. 
Beside the routine estimates of the number of bacteria recovered 
from the air, special studies were made of the length of life of the 
pheumococcus in the subway, the numbers of bacteria in subway and 
other dusts, the action of lubricating oil upon bacteria, the kinds of 
molds present, and the efficiency of various commercial deodorants 
and germicides intended for subway use. 
5 
Fic. 7.—Colonies of bacteria grown on a plate exposed fer fifteen minutes at the 
Grand Central subway station. 
RESULTS. 
A careful examination of the bacterial data collected in these 
studies, excepting the data which relate to the dust, has led me to the 
following conclusions: 
There were, on an average, more than twice as many bacteria found 
in the air of the streets as in the air of the subway, excepting after 
rains, when fewer were found outside than inside. 
The average numbers of bacteria which settled from the air in 
fifteen minutes, and were subsequently enumerated, were, in the sub- 
way, 500; outside, 1,157; difference, 657. (See fig. 8.) 
The average number of bacteria found by filtering the air was 3,200 
per cubic meter in the subway and 6,500 in the streets; difference, 
3,300. 
The molds recovered from the air by filters were almost always less 
numerous in the subway than out of doors. The maximum number 
