BACTERIOLOGICAL STUDY OF RETAIL ICE CREAM. 
13 
THE PEPTONIZING GROUP. 
The peptonizing group is probably the most interesting if not the 
most important group of bacteria in ice cream. This group consists 
of what are commonly known as the putrefactive bacteria; that is to 
say, they attack primarily the proteins, decomposing them into less 
complex organic bodies. Bacteria of this class are usually considered 
undesirable in articles of food, and it is to them that intestinal 
troubles are sometimes attributed, perhaps with or without justifica- 
tion. Whatever their true effect is will not be discussed in this 
paper, but because bacteria of this group are looked upon with sus- 
picion it is therefore of great importance. In Table 8 will be found 
the averages of the number of peptonizing bacteria in ice cream 
during the summer and winter seasons from a number of different 
plants. 
Table 8. — Average number of peptonizing bacteria per cubic centimeter of ice cream from 
various manufacturers. 
Summer. 
Winter. 
Manufacturer. 
Number 
of 
samples. 
Average 
number of 
peptonizing 
bacteria 
per cubic 
centimeter. 
Number 
of 
samples. 
Average 
number of 
peptonizing 
bacteria 
per cubic 
centimeter. 
A 
15 
7 
8 
6 
3 
3 
5 
1 
1 
1 
4 
4 
4 
2 
3 
1 
909, 132 
3,579,261 
2,752,681 
2,587,978 
1,064,463 
1,018,440 
567, 409 
328, 119 
406,400 
1, 128, 000 
415,018 
4,370,497 
874, 754 
72,253 
2, 879, 467 
247, 656 
3 
7 
2 
3 
30 358 
B 
1,159 sss 
c 
2,097 
247 944 
D 
E 
F 
3 
3 
104,008 
197 314 
G 
H 
I 
J 
2 
2 
290 623 
Ki 
117 316 
L 
M 
N 

P 
68 
1,449,533 
21,000,000 
36, 063 
25 
268 693 
2,974,400 
1,194 
The bacterial averages were much higher in the summer than 
during the whiter. It is evident from these figures that the average 
commercial ice cream contains a large number of peptonizing bac- 
teria. In order to show the range in the percentage of peptonizers, the 
entire lot of summer and winter samples has been plotted in a fre- 
quency curve, as shown iri figure 4. It will be seen that the majority 
of samples contained from 0.1 to 5 per cent of peptonizing bacteria. 
A large proportion contained, however, as high as 25 to 30 per 
cent, and in a few samples they were present to the extent of from 
90 to 95 per cent of all the bacteria. 
