ICE CREAM BACTERIA 437 
and remove samples from the interior of the mass of ice cream. This 
may be done by scraping off the exterior with a sterile spatula and by 
means of a sterile scoop transfer portions to sterile flasks. Heat these 
on a water bath at 40° C. with oceasional stirring until melted. Dilute 
with sterile pipettes and plate out using the standard media. 
Bacillus Typhosus in Ice Cream. Several severe epidemics of 
typhoid fever have been caused by ice cream. Mitchell (1915) found 
that these bacteria could live for 12 to 39 days in ice cream and that 
ice cream could thus become an important epidemiological factor in the 
spread of the disease. Cumming (1917) reported an epidemic of 
typhoid fever caused by a carrier who participated in the preparation 
of the cream. Lumsden (1917) has given the characteristics of epi- 
demics caused by ice cream. The difficulty of securing accurate data in 
such epidemics is mentioned. Waterman (1917) has reported a small 
outbreak of typhoid fever which probably came from ice cream; the 
typhoid history of the people involved is rather striking. Bolten (1918) 
reported experiments on freezing B. typhi in cream. At the end of a 
month the number of bacteria is reported to have been reduced to about 
one-twentieth of the original number. At the end of about 45 days 
after freezing in brine, some of the bacilli were found to be alive. As 
the author points out, ice cream may be a potent factor in the dis- 
semination of typhoid fever. 
Determination of the Number of Bacteria in Ice Cream (Esten 
and Mason). Samples are taken with sterilized knives, the outer layer 
being cut off before the sample is taken out. Allow the cream to melt 
at room temperature in the same manner as milk samples. Plate out 
on litmus lactose gelatin; incubate for 7 days at 21° C. and count. 
Make four plates from each sample and report the results as an average 
of the four plates. By using litmus lactose gelatin the number of acid- 
forming bacteria and the number of liquefying bacteria may be deter- 
mined. 
Savage’s Method for Bacterial Analysis of Ice Cream. 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 min- 
utes 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. 
Determination of Streptococci in Ice Cream (Wiley et al.). The 
method for the detection of streptococci in ice cream has been used by 
