430 
After careful consideration of the subject the following methods 
have given satisfactory results in this laboratory: 
The samples were always collected in the original containers, 
either pint or quart bottles being purchased for our purposes. Some 
of these samples were obtained from the wagon on the street, others 
from the dairy, and still others were obtained from houses in various 
parts of the city, at once after being delivered in the usual course of 
trade. It is therefore believed that the samples examined fairly rep- 
resent the average milk obtained by the householder. The samples 
were collected early in the morning and at once placed in a metal 
container filled with cracked ice. From six to eight samples were 
collected each morning from various parts of the city, and rarely 
more than two hours elapsed from the collection of the first sample 
to the time it was received in the laboratory. The temperature was 
taken with a good thermometer at the time the sample was col- 
lected, but always from a different bottle, which was afterwards 
used for chemical purposes. 
It was noted that after the milk stood on ice for some time that 
there might be a difference of 6 to 8 degrees between the top and 
the bottom layers of the milk in a pint bottle. The milk was 
always shaken well in order to mix the cream and to help break up 
the bacterial clumps before the bottle was opened, which was done 
with the usual bacteriologic precautions. For ordinary market milk 
the following dilutions were made: 
1 cubic centimeter milk + 99 cubic centimeters sterile water. 
0.1 cubic centimeter of this was used for the first plate, which rep- 
resented 1:1,000. 
0.5 cubic centimeter of the first dilution was then added to 49.5 
cubic centimeters of sterile water. One cubic centimeter of this dilu- 
tion when plated represented 1:10,000, and 0.1 cubic centimeter of 
this dilution represented 1:100,000. 
The dilutions were vigorously shaken at least twenty-five times in 
accordance with the standard methods for water analysis in order to 
obtain uniform suspension of the bacteria. Sterile distilled water was 
used as a diluent. 
The final dilution was measured directly into a petri dish and agar 
poured at a temperature of between 40° and 45° C. in the usual way. 
After the plates were well set, they were grown at 37° C., which 
temperature appears not only to favor the maximum growth of 
bacteria ordinarily found in the milk, but has the additional advan- 
tage of favoring the kinds of bacteria belonging to the pathogenic 
class. The plates were counted at the end of twenty-four hours, 
although by that time the maximum growth had not appeared. 
