439 
class. The plates were counted at the end of twenty-four hours, 
although by that time the maximum growth had not appeared. 
Only those colonies were counted which were visible to the naked 
eye or could be seen with a low-power magnifying glass. Three 
plates were always made from each sample, one from each dilution. 
Plates that became spoiled owing to spreading of the surface growths 
over them, irregular distribution, or excessive numbers, were dis- 
carded. The counts were always taken when possible from plates 
containing 200 or less bacteria per plate, the reading being reduced 
to round numbers. 
The composition of the media used for this work was 1.5 per cent 
agar and an acidity of + 1.5 to phenolphthalein as an indicator. 
In accordance with this method a number of samples of milk 
bought on the open market in Washington were examined in the 
Hygienic Laboratory, P. H. & M. H. S., during the summer months 
of 1906-7, the results of which appear in the following tables: 
j Results of bacterial counts of market milk in Washington , 1906 and 1907. 
Name. 
Date. 
Samples obtained at — 
Tempera- 
ture of 
milk 
when ob- 
tained 
(° C.). 
Number of 
bacteria 
per cubic 
centimeter. 
[July 10.1907 
9 
8,000 
Ag 
July 22, 1907 
Wagon 
10.5 
69,000 
Aug. 5, 1907 
Dairy 
9 
2, 680,000 
l Aug. 19.1907 
do 
6 
170,000 
[July 15,1907 
17 
2, 240, 000 
All 
July 30.1907 
Providence Hospital 
22 
5, 150, 000 
| July 31,1907 1 
do 
n 
111,000,000 
l Aug. 30,1907 
Dairy 
23 
190,000 
\1 
[July 11,1907 
18.2 
1,700,000 
Lug. 26,1907 
i Dairy 
7. 5 
1,090,000 
Alt 
[Aug. 1,1907 
1 do 
19.5 
22,500,000 
Lug. 27,1907 
do 
14 
2, 400, 000 
Am 
[July 12,1907 
26.5 
26,000,000 
Lug. 7, 1907 
Dairy 
24 
870,000 
['July 24,1907 
do 
20 
350,000 
Art 
July 29,1907 
Wagon 
20 
2,560,000 
Lug. 20,1907 
do 
13 
950,000 
Av 
(Aug. 30,1906 
Dairy 
14.5 
18, 300, 000 
T> 
ljuly 13,1907 
16 
3, 660, 000 
Jd 
Aug. 6, 1907 
Wagon 
27 
1, 000, 000 
Ba 
[July 16,1907 
do 
21 
2,800,000 
Lug. 2,1907 
do 
19 
880,000 
[July 12,1907 
10 
700,000 
Bee 
(July 22,1907 
12 
2,180,000 
[Aug. 14,1907 
i Dairy 
7 
11, 700, 000 
Lug. 28,1907 
do 
7 | 
320,000 
Aug. 6, 1906 
Wagon 
18 
1,380,000 
Sept. 5,1906 
Dairy 
8 
166,000 
Be 
Wagon 
11 
260,000 
July 6,1907 
22 
34,000 
Aug. 8, 1907 
i Dairy 
20 
23,600.000 
Lug. 20, 1907 
1 17 
94,000 
