THE BACTERIOLOGY OF ICE CREAM 197 



up 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 21 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 fairly 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 



"Bull. 134. 



