AIR OF NEW YORK SUBWAY—SOPER. 667 
ferent hours, it was impossible to calculate just how frequently the 
air was renewed; but from such estimates as it was possible to make 
it seemed not fannie that the air of the whole subway was com- 
pletely renewed at least every half hour. 
It is true that the renewal occurred somewhat more frequently in 
some parts of the subway than in others, but the exchange was always 
and everywhere abundant to satisfy usual sanitary requirements. We 
must except, of course, from this statement, the cars when closed, and 
other places where dense crowding occurr adi 
The controlling condition which regulated the extent to which the 
air was renewed was the freedom with which it could move in and out 
of the subway. The air was best where the subway was most open to 
the streets, and, conversely, it was least satisfactory where the subway 
was most inclosed. More blowholes would have greatly improved 
the conditions as regards heat and odor. 
The movement of the trains set in motion the essential ventilating 
currents. This they did, first, by forcing subway air out and bring- 
ing street air in at openings; and second, by moving the air through 
the subway between openings. 
It was fully demonstrated that there were no pockets or other places 
where air stagnated. Diffusion was everywhere rapid, complete, and 
satisfactory. I except the cars in these statements, as already indi- 
cated. 
The fact that there were only about half as many bacteria found in 
the air of the subway as in the air of the streets under which the sub- 
way ran gave ground for the opinion that the bacteriological condi- 
tion of the subway air was satisfactory, although too much reliance 
should not be placed upon this guide to its condition. Judgment on 
this point would have been more conclusive had it been possible to 
demonstrate that no more harmful bacteria existed in the subway than 
in the air outside. This was beyond the practicable possibilities of 
bacteriological technique. 
The odors of the subway, like the heat and dust, were objection- 
able, apparently, chiefly because they were disagreeable. They re- 
sulted largely from the operation of the trains. They were, in my 
opinion, to a large extent preventable. 
The sanitary significance of the characteristic black dust of the 
subway, containing, as it did, over 61 per cent of metallic particles, 
remained to be considered at the close of the investigation. At the 
request of the board of rapid transit commissioners, this matter is now 
being studied by me. 
