RELATION OF MICROORGANISMS TO SPECIAL DAIRY PROPUCIS 447 



ing the milk and holding it in a frozen condition. The process has 

 proved to be rather expensive and not very satisfactory. One difficulty 

 with this process seems to be that the quaUty of the frozen milk after it 

 has been melted is not as good as it was before it was frozen. From a 

 bacteriological standpoint, this process is of some interest, but it is 

 doubtful whether it becomes of much importance commercially. 



Ice Cream 



Ice cream is one of the important manufactured dairy products and 

 its use seems to be increasing steadily. Its bacterial flora varies with 

 the materials used in its manufacture and the conditions under which it 

 is made. It may be made from fresh cream which is only a few hours 

 old and under good sanitary conditions. On the other hand, it may be 

 made from cream which has been produced and handled under unsani- 

 tary conditions, kept in storage for a number of days and finally manu- 

 factured in surroimdings not conducive to a low bacterial content. We 

 are not surprised, therefore, to find a very wide variation in the germ 

 content of ice cream, as it is placed upon the market. 



An examination of 263 samples of ice cream collected in the city of 

 Washington* showed an average germ content of over 26,600,000 per 

 C.C. The lowest count obtained was 37,500 and the maximum was 

 365,000,000. A similar study of commercial ice cream in Philadelphiaf 

 showed the average bacterial content to be very high. The lowest 

 coimt found was 50,000 per c.c, while the highest count was 150,200,000. 

 In this work it was found that the bacterial content of the ice cream was 

 in quite direct relation to the sanitary conditions of the establishment 

 where the ice cream was manufactured. When ice cream is manufac- 

 tured in a city from materials which have been shipped in from consider- 

 able distances and frequently held for several days in cold storage, it is 

 not surprising that the germ content of the manufactured product 

 should be high. In some establishments the cream is pasteiurized be- 

 fore manufacturing, while in others it is used in its raw condition. 



In normal cream held for sometime, the lactic bacteria should exist 

 in considerable numbers, but when cream is held at low temperatures 

 these organisms do not develop rapidly. Peimington found that cer- 



• Results of work done under the direction of G. W. Stiles, 

 t Work done under the direction of Dr. M. E. Pennington. 



