BACTERIOLOGICAL STUDY OF EETAIL ICE CREAM. 7 
furnish evidence that ice cream can be made commercially, at least 
under some conditions, with a low bacterial content. If these aver- 
age counts are compared with the average counts from other cities, 
as shown in Table 1, it will be seen that, so far as bacteria are con- 
cerned, the quality of the ice cream is about the same in different 
localities. 
THE GROUPS OF BACTERIA. 
THE GENERAL GROUPS. 
The bacteria in 71 summer samples and 28 winter samples of ice 
cream were divided into groups by the milk- tube method of differen- 
tiation heretofore mentioned. With this method it was possible, 
/.se% 
Fig. 2.— Average bacterial groups found in one cubic centimeter of ice cream during the summer months, 
showing percentages of groups. 
Group. Bacteria per c. c. 
Acid-coagulating 18, 861 , 805 
Acid-forming 7, 844, 575 
Inert 5 , 292 , 815 
Alkali-forming 704, 195 
Peptonizing 5, 156, 519 
Total 37, 859, 909 
on the basis of the 14-day reaction in litmus milk, to divide the 
bacteria into five groups, namely, acid-coagulating, acid-forming, 
inert, alkali-forming, and peptonizing. For convenience in obtaining 
a view of the average groups in an average sample of ice cream, the 
results are presented graphically. Figure 2 represents 1 c. c. of ice 
cream and is divided into five sectors, each representing the average 
percentage of a group of bacteria. The averages are based on the 
analyses of 71 samples of ice cream examined during the summer 
season. It may be seen from the figure that the bacteria of 1 c. c. of 
