12 
BULLETIX 342, U. S. DEPARTMENT OF AGRICULTURE 
expected to conform exactly to these 
averages. Variations in methods and 
conditions in the production of milk 
may influence considerably the bacte- 
rial group relations of an individual 
sample. 
pose. As the milk stands, the acid 
formers grow and cause the milk to 
sour instead of decompose. When 
milk is Pasteurized at 180° F. for 30 
minutes, however, the bacteria (lactic- 
acid) which cause the souring of milk 
&41Y 
M/LX-. 
Af/l/f &tSrSV/?/Z£0 f&J? SO A?/A/C/T£S s4T 
. A 
S9CTO 
/JC/D 
M£WT 
GffOC//? 
W7VMZ/WG 
enow? 
m 
' 62.8°C. 7/./°C 76.7°C. 
f/45°X} f/€0°/Tj (/70°/Tj 
% 
^ 
» 
^s 
\\ 
\s. 
ft 
& 
1 
h?j 
li 
ii \ 
ill'! 
^ 
^ 
s* 
^ 
! 
j 
^ 
^ 
!^ s 
1 
f 1 
$ 
1 llll 
SS 
si 
If 
82.2°C. 
(/&o°/r) 
87.8?C 
S3.3°d. 
Fig. 1. — The hypothetical relation of the bacterial group to raw and Pasteurized milk 
The results in Figure 1 may perhaps 
be 1 >etter explained in popular terms. 
"When milk is Pasteurized at 145° F. 
for 30 minutes, most of the bacteria 
(lactic-acid) left alive in it are of the 
kind which cause it to sour, and there 
are present only a few bacteria (pep- 
tonizing) which cause it to decom- 
are practically all destroyed, and those 
which are alive (peptonizing) continue 
to grow and cause the milk to decom- 
pose. 
Not only do certain types of lactic- 
acid bacteria survive Pasteurization 
but some also grow at the Pasteuriz- 
ing temperature. Sometimes upon 
