376 
Journal of Agricultural Research 
Vol. XXVI, No. 8 
The milk was then plated out as follows: After thorough agitation 
o.i cc. was removed in a o.i cc. precision pipette and added to ioo cc. of 
sterile normal salt solution in a sterile flask. After thorough mixing, 
i cc. of this solution was then transferred to each of two sterile Petri 
dishes, sterile nutrient agar added, and the contents thoroughly mixed. 
This gave a i :iooo dilution of the milk and was found to be satisfactory 
so far as the counting of the colonies was concerned. In a few instances 
it was necessary to estimate the number of colonies by counting the 
colonies in 12 square centimeters and multiplying the average number 
by the area of‘ the plate. In doing this a Bausch and Lomb colony 
counter was used. In the majority of cases, however, the actual num¬ 
ber of colonies could be determined. 
In all tests the plates were kept at 37.5 0 C. for 48 hours before being 
counted. In the earlier tests fermentation tubes containing 1 per cent 
lactose broth were used to indicate B . Coli, but later the milk was plated 
out with Bacto-purple lactose agar. While this medium is also affected 
by Streptococcus lactis , the colonies of this organism can be differentiated 
readily from those of B. Coli. 
Chlorin was first used as a solution of sodium hypochlorite, part of 
the time as a chemically pure solution prepared in our laboratory, part 
of the time as the commercial product “BK.” The chlorin water used 
was made in the laboratory, as was some of the solution of calcium 
hypochlorite, though some high grade “bleach ’* or “chlorid of lime" 
was also used. All of these solutions were carefully titrated against 
an arsenic trioxid solution to determine the amount of active chlorin 
each contained at the time used. 
Since the solution of “BK” was alkaline, two series of tests were made 
simultaneously. In one, the alkaline solution was used (Table II), and 
in the other the neutralized solution (Table III). 
Table II. —Action of sodium hypochlorite (“BK”)—alkaline 
Active chlorin. 
Time acting 
before plating. 
Bacteria. 
Gas in lactose 
broth. 
Flavor of 
chlorin. 
Untreated. 
1 1 500 . 
i hour. 
...do. 
2, 160, OOO 
IOO 
10 per cent. 
None. 
Yes. 
1:2500 .. 
...do. 
6,000 
...do. 
Trace. 
115000. 
...do. 
7, 200 
10, 700 
16, 500 
.. .do. 
Do.. 
1 * 2 5000 . 
...do. 
...do. 
None. 
1:50000 . 
...do. 
5 per cent.. 
Do. 
Table III. —Action of sodium hypochlorite (“ BK”)—neutralized 
Active chlorin. 
Time acting 
before plating. 
Bacteria. 
Gas in lactose 
broth. 
Flavor of 
chlorin. 
Untreated .. 
1 hour. 
2,160, OOO 
10 per cent. 
None. 
... do. 
0 
Trace. 
... do. 
4, 800 
7 > 25 <> 
IO, OOO 
. . .do. 
Do. 
...do. 
J Trace. 
Do. 
I * ^OOO ♦ . 
...do. 
!... do. 
None. 
.1*25000 . 
T * cj<?<yv>. 
...do. 
13, 500 
!...do. 
Do. 
! 
