328 
Journal of Agricultural Research 
Vol. II, No. 4 
The second class of streptococci survive Pasteurization because of the 
fact that their majority thermal death point is above the Pasteurizing 
temperature. As previously stated in this paper, the writers isolated a 
lactic-acid streptococcus from Pasteurized milk which required 30 min¬ 
utes' heating at 75.6° C. (168 0 F.) to destroy it. During the summer of 
1909 some experiments were made to determine the effect of Pasteuriza¬ 
tion for 30 minutes on this culture at various temperatures. In Febru¬ 
ary, 1914, after having kept this culture by repeated transfers in sterile 
milk, the experiment was again repeated. As may be seen from Table 
IV, in the experiments in 1909 there was no reduction of bacteria of this 
culture when Pasteurized for 30 minutes at 6o° C. (140° F.) or 65.6° C. 
(150° F.), but there was a reduction of 53.07 per cent when heated at 
71.1 0 C. (160 0 F.) for 30 minutes. 
In the repeated experiment with the same culture, about 4X years 
later, similar results were obtained. At 6o° C. (140° F.) and 65.6° C. 
(150° F.) there was practically no reduction in the bacterial numbers. 
The slight difference noted is within the experimental error, as this 
culture grows with difficulty on solid media. At 71.i° C. (160° F.) 
there was a reduction of 99.20 per cent. 
This organism has a high majority thermal death point, as may be 
seen from these results, and is able to survive Pasteurization because its 
majority thermal death point is above the temperature of 62.8° C. 
(145 0 F.), the temperature generally used in commercial Pasteurization 
with the holder process. It is also interesting to note that the ability 
to resist high temperatures is a permanent characteristic of this organism. 
(See Table IV.) 
Tabl3 IV .—The majority thermal death point of a lactic-acid forming streptococcus 
EXPERIMENT DURING SUMMER OP 1909 
Temperature. 
6o° C. (140° F.) 
65.6° C. (150° F.) 
71.i° C. (160 0 F.) 
Number of bacteria per c. c. 
Percentage of 
Before heating. 
After heating. 
reduction. 
f 58, OOO, OOO 
63, OOO, OOO 
1 
< 64, 500, OOO 
[ 0 61, 250, OOO 
51, OOO, OOO 
a 5 7,2$°, 000 
1 ° 
41, OOO, OOO 
41, 700, OOO 
0 
f 244, OOO, OOO 
\ 315,000,000 
[ <*284, 500, OOO 
133,000, OOO 
138,000,000 
a 135> 5°°> 000 
53-07 
® Average. 
