July 15, 1925 
Cleaning Milking Machines 
193 
As noted in Tables I, II, and III, the average bacterial counts 
on samples of milk drawn with the machine which was sterilized 
by the heat method were all very uniform, only one count going 
higher than 10,000 per c. c. There was very little difference be¬ 
tween the results obtained by the chloride of lime method and by 
the brine or salt and chloride of lime method, during the cold weather. 
The results were very good, although not so good as those obtained 
by the heat method. During the warm weather, however, the bac¬ 
terial counts accompanying the chloride of lime method and the salt 
and chloride of lime method rose considerably. Of the two methods 
the salt and chloride of lime method gave much better results than 
the chloride of lime. This was evidently due to the presence of the 
salt, which undoubtedly acted as a stabilizer in keeping the available 
chlorine from being given off too rapidly. However, the salt and 
chloride of lime had a marked corrosive action on some of the metal 
E arts of the milker, which the heat method and plain chloride of 
me solution did not have. 
For a short period during one month the machines were used for 
two milkings a day, and during this time the unit which was sterilized 
with heat was placed in the hot water (160° to 165° F.) after it 
was washed and allowed to remain there until the next milking, the 
water cooling off gradually. The other two units were treated as 
formerly, being placed in their respective solutions after they were 
washed, and allowed to remain there until the next milking. Seventy- 
five samples of machine-drawn milk from each unit were collected 
during the month, 45 of which were from once-a-day milking and 30 
from twice-a-day milking. Results are given in Table IV. 
Table IV .—Comparison of bacterial counts from milking once and twice a day 
Once-a-day milking 
Twice-a-day milking 
Method 
Number 
Average 
Number 
Average 
of sam¬ 
bacterial 
of sam¬ 
bacterial 
ples of 
count 
ples of 
count 
milk 
per c. c. 
milk 
per c. c. 
. - 45 
2,380 
30 
2,450 
Chloride of lime--- 
45 
5,220 
30 
5,160 
Salt and chloride of lime_ _____ 
45 
5,280 
30 
5,240 
As noted in Table IV, there was practically no difference between 
the bacterial counts of the once-a-day and twice-a-day milking 
samples under the same sterilizing treatment. 
All units were used for about 120 milkings, no rubber parts were 
replaced on any of them during this time, and all were still in good 
condition at the end of the experiment. Bacterial counts were 
made on samples of the sterilizing solutions of chloride of lime, and 
salt and chloride of lime, taken from the long milk tube. These 
counts varied considerably. There was no correlation between the 
age or bacterial counts of the solutions so taken and of the bacterial 
counts of the milk samples taken on the same days during the cold 
weather. During the warm weather, however, there was a direct 
relation (with one exception) between the age of the solution and the 
bacterial counts of the milk: the older the solution the higher the 
counts of the milk. A summary of the results is shown in Tables V 
and VI. 
