Oct. 1. 1925 
Bacterial Count of Milk and Cream 
697 
over the whole milk occurs with milk of low bacterial count. The 
greatest per cent of decrease also occurs with low-count milk. Part 
of this variation is possibly due to limits of laboratory error, 
which would be more pronounced in a low-count than in a high- 
count milk when figuring percentage increases and decreases. 
Table IV gives the grouping of the samples according to bacterial 
count, together with the percentage relationship of the counts of 
the cream and whole milk by bacterial groups. 
Table IV .—Per cent increase and decrease of bacterial counts of cream and whole 
milky classified by grouping of whole milk bacterial count 
Bacteria per cubic centimeter 
Increase in cream 
over whole milk 
Decrease in cream 
under whole milk 
Number of 
samples 
showing no 
change 
i 
Number of 
samples 
Average 
per cent 
Number of 
samples 
Average 
per cent 
Oto 50,000..... 
37 
28.07 
t2 
15.907 
6 
50,001 to 100,000..... _ 
17 
25.2 
3 
13.13 
1 
100,001 to 500,000. _ 
4 
14.82 
4 
14.722 
500,001 to 1,000,000. 
4 
10.245 
3 
9.396 
1 ,000,001 and over 
8 
10.936 
1 
6.06 
Total .. - . __ 
70 
23 
1 
7 
Out of a total of 70 samples showing an increase in the bacterial 
count of the cream over the whole milk, 64 samples (or 91.4 per 
cent) gave an increase of 50 per cent or less. In no instance was there 
a greater increase than 90 per cent. All of the 23 cream samples 
wmch showed a decrease in the count under that of the original 
whole milk gave a decreased count of 50 per cent or less. 
From the work which has been presented, it would seem that there 
is no basis of fact for the assumption that the bacterial count of 
centrifugally separated cream should be several hundred per cent 
higher than the whole milk from which it is derived, provided the 
separator is clean. 
GRAVITY SEPARATION 
For this work a gravity separation can 18 inches high and 8J^ 
inches in diameter was used. At the bottom was placed a pet cock 
to draw off the skim milk. A small strip of glass was inserted in 
the side, extending upward from the bottom of the can sufficiently 
so that the dividing line between the cream and skim milk could be 
observed. As a means for holding the milk in the separator at a 
low temparature, the can was placed in a large tank with sufficient 
ice and water around it to extend above the depth of the milk in 
the can. 
Before the separator can was used it was thoroughly washed with 
hot water containing a strong solution of washing powder, then 
thoroughly rinsed, and finally inverted over a steam jet and allowed 
to steam for five minutes. The cover was cleaned and steamed 
in the same manner. After steaming, the cover was placed on the 
can and the separator was aUowed to cool. Fresh mixed-herd milk 
was then placed in the separator. Samples for bacterial count and 
fat content were taken. The can was then set into the cooling and 
