186 UNIVERSITY OF WISCONSIN STUDIES 
cent, acid-forming 38.03 per cent, inert 4.81 per cent, alkali- 
forming 5.42 per cent and peptonizing 20.90 per cent. In 
general these were high count ice creams and would be ex- 
pected to show a considerable percentage of acid producing 
organisms. 
The occasional presence of pathogens in ice cream is evi- 
dent from the cases of disease that have been traced to this 
product and is to be expected, due to the presence of these 
types of organisms in cream. 
It ig evident that ordinarily the types of bacteria found in 
ice cream are determined practically entirely by the sanitary 
quality of the materials used and by the handling given and 
that the range in flora is limited only by the extent of varia- 
tion that is possible with these. 
Tur Sources oF THE BacTEerRIA IN Ick CREAM 
The bacteria that are present in ice cream come from two 
main sources: (1) the materials used and (2) outside con- 
tamination. 
(1) The Materials Used 
Cream. The cream used in the manufacture of ice cream 
is quite likely to carry many bacteria unless pasteurization is 
used, since ice cream manufacturers ordinarily buy cream 
under conditions such that they have little, if any, control 
over the methods of production. Commonly also considerable 
difficulty is experienced in securing sufficient sweet cream ; 
this is particularly true during the hottest months when the 
demands on the manufacturer are heavy. Accordingly, the 
ice cream factories in certain sections are sometimes virtually 
forced to accept cream with practically no other requirement 
than that it be sweet and, in certain cases, the ice cream sold 
is ample evidence that this requirement is not rigidly adhered 
to. A portion of this cream is shipped without refrigeration 
facilities and, although pasteurization before shipment is quite 
common, it inevitably arrives at the ice cream factories with 
enormous numbers of bacteria. 
