METHODS OF ANALYZING AIR OF PAVEMENTS FOR BACTERIA. 
The bacteriological examinations were carried on by means of using 
the agar plate exposure, four-inch Pasteur dishes being used. These 
agar plates were exposed (always in duplicates) on an ordinary sur- 
veyor’s tripod, as shown in Fig. 1. This made the exposure about five 
feet above the pavement. Half way between the exposed plates and the 
pavement hung the anemometer, which had to be used to determine differ- 
ences in wind velocities from minute to minute. These plates were al- 
Ways exposed for exactly ten minutes, and careful notice taken of the 
amount of traffic, direction of wind, and anything that would affect the 
amount of floating dust. Great care was taken to see that the wind was 
blowing as nearly parallel to the street as possible, so that the analysis 
would surely be of the street dust, and not of the dust from the adjoining 
lots. 
One set of exposures was made between 12 and 2 o’clock at night when 
the life on the streets would be at a minimum. The results of this set 
of plates were as follows, the numbers indicating the number of bacterial 
colonies on each agar plate that had had an exposure of ten minutes: 
Wood block (umerecosoted) VPlare INOM a. or csr e ee, creer 50 
Brick PIG INOW eee ooo etaa ey Sites ote oh area sii Venere Lan ee ee 16 
Sheet asplialt,, PlateiNow Ze cece ois, wince. solu aleyer sev oloteee oie eter stenees 14% 
Macadamt, (Plate NOM dics ute oe cctools tie ech. eines Sets ene 915 
The numbers indicate the average number of bacterial colonies on the 
two plates that were exposed side by side over each pavement. 
Another interesting set of exposures was made at a time when the 
macadam street was muddy, the brick pavement was fairly dry, except 
for moisture in the interstices, and the sheet asphalt was dry. <A drizzling 
rain had occurred about twenty-four hours previous to the exposure. 
Results as follows: 
Sheet. asphalt,. Plate-INo:- dlc. &.. ito beats odtoeeis cates neeereeaneee 2850 
MCCAIN a5 5.5 & wo ise Sec ie ste d'e8 Seemed ee oe is thao Ieee 147 
Brick: "Plate: NOs 13s sit 2 Sa ee og ee Ree eae 99 
In this exposure it was evident that the sheet asphalt pavement had 
become quite dry and the dust was stirred up to a very considerable de- 
