138 BACTERIOLOGICAL METHODS 



used. If stronger solutions are used, many of the tubercle bacilli 

 are also disintegrated or considerably changed in form and in the 

 behavior with the acid-fast stains. 



In addition to the routine examination of ice creams for the 

 presence of fillers and ingredients which do not properly belong 

 to ice creams, the food bacteriologist will have occasion to make 

 bacteriological and toxicological tests. According to Vaughan, 

 the toxic changes in ice cream are due to the presence of a poison 

 designated tyrotoxicon, presumably identical with the toxin occa- 

 sionally found in milk and cheese. Ice-cream poisoning depends 

 upon the development of the toxin-forming bacteria in the milk 

 and cream before it is frozen. It is not at all likely that ice cream 

 made from clean wholesome cream and milk will contain toxins, 

 provided it is kept well frozen and is not stored too long. There 

 is good evidence that slightly infected ice cream which is kept for 

 several days and longer, may show sufficient toxic bacterial de- 

 velopment to produce symptoms of poisoning. The virulency of 

 the toxins produced by the bacteria appears to increase with the 

 lowering of the temperature. 



The danger from ice cream is directly proportional to the un- 

 sanitary conditions of the milk and cream used and ice-cream 

 poisoning is far more likely to manifest itself during the hot summer 

 weather. All suspicious ice creams should be examined bacteri- 

 ally, making numerical plate cultures and also the presumptive co- 

 lon bacillus test and tests for streptococci and staphylococci. The 

 toxicological test as recommended for meats, is, however, far more 

 important and should not be omitted. Ice cream should not con- 

 tain more than 1,000,000 bacteria per cc. and should not develop 

 colon bacilli in less than o.io cc. quantities by the standard pre- 

 sumptive colon bacillus test. 



Of the more common ice-cream fillers we may mention starch 

 and tragacanth. Vegetable mucilages other than tragacanth may 

 be suspected. Gelatin is also used. Eggs are frequently added. 

 A filler to which a small amount of rennet had been added has 



