BACTEEIOLOGICAL STUDY OP 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, 



AS6% 



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, 8G1, 805 



Acid-forming 7, 844,575 



Inert 5, 292, 815 



Alkali-forming 704, 195 



Peptonizing 5, 150,519 



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 samplo of ico cream, the 

 result , arc presented graphically. Figure 2 represents 1 c. c. of ice 

 cream and is divided into five sectors, each representing the avcrago 

 percentage of a group of bacteria; The averages are based on the 

 ilyses of 71 samples of ice cream examined during the summer 

 on. It may be seen from the figure that the bacteria of 1 c. c. of 



