120 MODIFIED MILK AND MILK PRODUCTS 



of this food and the prolonged period of cooling take place in 

 very many cases under most insanitary conditions. It is not 

 therefore to be wondered at that ice-cream is frequently found 

 to be very heavily contaminated with bacteria, and that a 

 number of outbreaks of illness has been reported from its use. 



The following data- from a valuable paper by Buclian 1 will 

 give some idea of the average bacterial condition of ice-cream : 



a b c 



Organisms per c.c. (averages) ... 867,000 13 millions 372 millions 

 Percentage showing : Percentages 



Coli group organisms in i c.c. or less 16 58 94 



" Enteritidis change" 10 c.c. or less 46 64 80 



ioo c.c. ... 82 92 96 



Streptococci in o'oi c.c. or less ... 6 36 68 



i ... 38 52 82 



a = fifty samples collected immediately after heating. 

 b= ,, ,, ,, at varying intervals after cooling had begun. 



c ,, ,, after the material had been frozen. 



Pennington and Walter 2 examined sixty samples of com- 

 mercial ice-cream in America, finding the number of bacteria to 

 vary from 50,000 to 151,000,000. Streptococci were found in 

 80 per cent, of the samples. 



Bacteriological examination. 



The ice-cream should be collected in a sterile vessel e.g., a 

 wide-mouthed sterile bottle with glass stopper and packed in 

 ice if it cannot be examined at once. 



To examine, melt the ice-cream by placing for fifteen to 

 twenty minutes in the 22 C. incubator, then treat as a milk 

 sample. 



The degree of dilution and the methods of examination are 

 similar to those used in the examination of milk. 



The examinations usually carried out are : estimation of 

 the number of bacteria, estimation of B. coli group organisms, 

 with identification if necessary of the chief kinds present, 

 enumeration of streptococci, estimation of spores of B. enteritidis 



1 Journ. of Hygiene, 1910, X, p. 93. 



8 New York Med. Journ. 1907, LXXXVI, p. 1013. 



