THE BACTERIOLOGY OF ICE CREAM 197 
mp and allowed to stand at a fairly high temperature before 
being frozen have been shown to give trouble in certain in- 
stances; this is to be expected especially when the material 
has been heated and the non-spore-forming acid producers 
destroyed, thus leaving the field free to the spore-bearing bac- 
teria. The long storage of cream at temperatures around 32° 
F. should be prevented because of the well-known chemical 
changes that occur in milk and undoubtedly in cream at such 
temperatures. The pronounced increase in the amount of 
soluble nitrogen is much more likely to result in the develop- 
ment of poisonous products than the decomposition of the 
lactose which takes place at higher temperatures and which 
by the development of acid keeps down the spore-forming 
peptonizing bacteria. The ice cream manufacturers have a 
real problem in their cream supply, particularly at times of 
fairs, holidays, etc., when the storage of cream for consid- 
erable periods of time is a practical necessity except in those 
exceptional districts where there is an abundant sweet cream 
supply. It seems, though, that safety demands a reasonable 
limit on the length of time that cream should be stored, even 
at such favorable storage temperatures as 32° F. 
Epidemics due to ice cream have been noted by various in- 
vestigators and have become common enough to no longer 
excite any unusual comment. The Iowa Agricultural Experi- 
ment Station™? cited some of the references previous to 1912 
which give an idea of the extent of the outbreaks up to that 
time. Since then, literature on the subject has continued to 
appear. The disease most commonly spread through ice cream 
is very evidently typhoid fever and some fairlv large epidemics 
of this disease have been traced to this source. There is no 
reason to doubt the claim that all diseases spread through 
milk can be spread through ice cream unless precautions are 
taken to prevent it. 
Undoubtedly, the most common method of the contamina- 
tion of ice cream is by bacillus carriers. Such individuals 
have frequently been found to be the cause of epidemics and 
4 Bull, 134. 
