448 MICROBIOLOGY OP MILK AND MILK PRODUCTS 



tain species of streptococci developed quite rapidly in cream held at 

 refrigerator temperatures. Streptococci were found in fifty-five (80 per 

 cent) of the sixty-eight samples examined. It was found that at refrig- 

 erator temperature^ the relative growth of these organisms was greater 

 than at higher temperatures, a fact which may account, in part at least, 

 for the frequency with which these organisms occur in ice cream. 



Frequently ice cream is held -for a considerable time in a frozen con- 

 dition before it is sold. It has generally been supposed that there is no 

 bacterial growth in material which is held below the freezing tempera- 

 ture. This, however, did not seem to be the case in samples examined 

 by the investigators already mentioned. They found in samples held 

 about a month that there was normally a decrease in the bacterial count 

 and also in the amount of gas production for a number of days, after 

 which there was frequently a marked increase in the bacterial counts. 

 These results would seem to indicate that even in the frozen condition 

 there may be some increase in the number of bacteria present. The 

 nurnber of these experiments, however, is not sufficient to justify very 

 general conclusions. The work of Conn and Esten* in holding milk at 

 1° may throw some light upon this question. 



If the cream from which the ice cream is made has been produced 

 and handled under sanitary conditions, the bacterial content should 

 consist chiefly of organisms of the Bact. lactis acidi type, in which case 

 the high count in the ice cream might not be objectionable. If, on 

 the other hand, the cream has been held in cold storage for some time 

 under conditions which inhibit the growth of the lactic organisms and 

 permit the development of putrefactive types, bacterial poisons may 

 be developed in the cream, which will be highly objectionable. There 

 seems to be little doubt that this is the cause of the cases of ptomain 

 poisoning, resulting from the use of ice cream. It is known that certain 

 types of bacteria, especially those belonging to the so-caUed putre- 

 factive group, are capable of developing at very low temperatures and 

 can, therefore, produce considerable quantities of toxic products in 

 the cream. Whether or not these products are developed before 

 the cream is manufactured or whether they may develop in the frozen 

 product cannot at present be stated. In general it can be said that the 

 total bacterial count does not indicate the wholesomeness of the ice 

 cream any more than does a similar count in buttermilk or in the com- 



* Annual Report, Stoir's Experiment Station, 1901. 



