July is, 1914 
Pasteurization of Streptococci 
329 
Tabl# IV .—The majority thermal death point of a lactic-acid forming streptococcus —Con. 
EXPERIMENT DURING WINTER OP 1914 
Temperature. 
Number of bacteria per c. c. 
Percentage of 
Before heating. 
After heating. 
reduction. 
6o° C. (140 ° F.). 
f 1, 400, OOO 
| 1, 600, OOO 
1, 040, OOO 
1,180, OOO 
O 
65.6° C. (150° F.). 
l 1, 500, 000 
a 1, $oo, OOO 
a 1, no, OOO 
1,310,000 
I, 200, OOO 
. 
71.i® C. (160 0 F.). 
a 1, 500, OOO 
a 1, 250, OOO 
II, 700 
J 
99. 20 
® Average. 
SUMMARY AND CONCLUSIONS 
(1) The thermal death points of 139 cultures of streptococci isolated 
from cow feces, from the udder and the mouth of the cow, and from milk 
and cream showed a wide variation when the heating was performed in 
milk for 30 minutes under conditions similar to Pasteurization. 
At 6o° C. (140° F.), the lowest Pasteurizing temperature, 89 cultures, 
or 64.03 per cent, survived; at 62.8° C. (145 0 F.), the usual temperature 
for Pasteurizing, 46, or 33.07 per cent, survived; and at 71.i° C. (160° F.) 
2.58 per cent of the cultures survived; all were destroyed at 73.9 0 C. 
(i6 5° F-). 
(2) The streptococci from the udder were, on the whole, less resistant 
and those from milk and cream more resistant to heat than those from the 
mouth of the cow and from cow feces. When heated to 6o° C. (140° F.) 
all of the 18 culturesfrom milk and cream survived; at 62.9°C. (i45°F.) 17, 
or 94.44 per cent, survived; at 68.3° C. (155 0 F.) 9 cultures, or 50 per cent, 
withstood the heating process. All the streptococci from milk and cream 
were destroyed by heating to 73.9 0 C. (165° F.) for 30 minutes. 
(3) Among the 139 cultures of streptococci there were 22 that 
formed long chains, which, for the purpose of this paper, were considered 
as typical streptococci. The others were considered atypical. The 
typical streptococci were much less resistant to heat then were the atypical. 
Of the 22 typical streptococci 12, or 54.54 per cent, survived heating 
for 30 minutes at 57.2 0 C. (135 0 F.); at 6o° C. (140° F.) 9, or 40.91 per 
cent, survived; at 62.8° C. (145 0 F.) only 1 culture, or 4.54 per cent, 
withstood the heating. All of the typical streptococci were destroyed by 
heating for 30 minutes at 65.6° C. (150° F.). 
The 117 atypical streptococci were more resistant; at 6o° C. (140° F.) 
68.37 per cent survived; at 62.8° C. (145 0 F.) 38.46 per cent survived; 
and at 71.i° C. (160° F.) 2.56 per cent survived; all were destroyed at 
at 73.9 0 C. (165° F.). 
