326 
Journal of Agricultural Research 
Vol. II, No. 4 
atypical. Of the 22 typical streptococci 17 were from udders and 5 from 
cow feces. 
The results in Table III show that the typical streptococci were less 
resistant to heat than were the atypical. Of the 22 typical cultures 12, 
or 54.54 per cent, survived 57.2 0 C. (135 0 F.). At 6o° C. (140° F.) 9 
cultures, or 40.91 per cent, withstood the heating. When heated to 
62.8° C. (145 0 F.) 1 culture, or 4.54 per cent, survived, and all were 
destroyed at 65.6° C. (150° F.). This culture was isolated from cow 
feces. It is, of course, possible that if a larger number of cultures had 
been used some would have been found which would have withstood 
heating to higher temperatures. 
Among the atypical cultures a much higher percentage were resistant 
to the higher temperatures. At 54.5 0 C. (130° F.) 99.14 per cent sur¬ 
vived. When heated to 6o° C. (140° F.) 68.37 P er cent withstood the 
temperature. At 62.8° C. (145 0 F.) 38.46 per cent survived, and at 
65.6° C. (i50°F.) 22.22 per cent still survived. Even at 71.i° C. (i6o°F.) 
3 cultures, or 2.56 per cent, withstood the heating. All were destroved 
at 73.9 0 C. (165° F.). See Table III. 
Table III .—Effect of heat on streptococci—cultures classified as typical and atypical 
Cultures surviving after heating for 30 minutes at— 
Classification of cultures. 
48.9° C. 
(120 0 F.). 
5i-7° C. 
(i2S° F.). 
54-5 6 c. 
(130* F.). 
57-2° C. 
(135° F.j. 
60“ c. 
(mo- F.). 
Typical,... 
Atypical... 
. 
[Number,. 
" \Per cent.. 
[Number.. 
' *\Per cent.. 
22 
100 
117 
100 
23 
IOO 
117 
IOO 
22 1 
IOO 
116 
99-41 
| 12 
54- 54 
106 
90. 59 
9 
40.91 
80 
68.37 
Cultures surviving after heating for 30 minutes at— 
Classification of cultures. 
62.8° C. 
(145 0 F.j. 
65.6° C. 
(150° F.). 
68.3 d C. 
(*55° F.). 
71.i° C. 
(160 0 F.). 
73-9° C. 
(165° F.). 
Typical.... 
Atypical... 
[Number.. 
‘ '\Per cent.. 
/Number.. 
■ ‘\Per cent.. 
1 
4* 54 
45 
38. 46 
0 
0 
26 
22. 22 
0 
0 
13 
11.11 
0 
0 
3 
2. 56 
0 
O 
0 
O 
This marked difference in the heat resistance of typical and atypical 
streptococci is more clearly shown in figure 3. 
Only 1 out of 22 cultures of the typical streptococci survived Pas¬ 
teurization at 62.8° C. (145 0 F.) for 30 minutes. As shown in figure 3, 
the atypical cultures were much more resistant to heat. 
From the results of these experiments it is evident that there is a con¬ 
siderable variation in the ability of streptococci to survive Pasteurization, 
and a general consideration of this ability seems of interest. 
