184 UNIVERSITY OF WISCONSIN STUDIES 



able importance have been observed. Ayers and Johnson 3 

 working in Washington, D. C. found that 94 samples of ice 

 cream examined during the summer months showed counts 

 from 120,000 to 510,000,000 with an average of 37,859,907 

 p?r c. c., while 91 samples examined during the winter months 

 ranged from 13,000 to 114,000,000 and averaged 10,388,222 

 per c. c. 



The great bulk of the ice cream manufactured in the U. S. 

 is vanilla ice cream and accordingly this is the type that 

 has been dealt with in most of the bacteriological examinations. 

 The Iowa Agricultural Experiment Station 4 has found that 

 the bacteriai content of ice cream other than vanilla is es- 

 sentially the same as that of vanilla and this finding is sub- 

 stantiated by data published by various laboratories. Water 

 sherbets, on the contrary, contain comparatively small num- 

 bers of bacteria; the Iowa Agricultural Experiment Station 4 

 found in 17 samples that the counts ranged from 6 to 7,800 

 per c. c. with 110 evident relationship between the bacterial 

 count and the flavor. The small numbers of bacteria in water 

 sherbets are undoubtedly due to the "fact that cream is not 

 employed in the manufacture, although the acid that is or- 

 dinarily present in these products may also play a part in 

 keeping down the count by destroying certain organisms. 



Because of the viscosity, the high percentage of solids, and 

 the large part of the solids made up of fat, the distribution 

 of the organisms in melted ice cream is perhaps never as 

 uniform as in a sample of milk. Duplicate determinations 

 made on unbroken containers of ice cream agree very well 

 however. In a comparison of 17 duplicates the Iowa Agri- 

 cultural Experiment Station 5 found variations from .79 per 

 cent to 22.73 per cent with an average of 6.75 per cent. On 

 broken containers from which ice cream was being dipped, 

 however, much higher variations were found, one of 137.19 

 per cent being recorded. Ayers & Johnson 6 have more re- 



8 IT. S. Dept. of Agriculture, Bulletin 303. 



4 Unpublished data. 



Bulletin 134, p. 298. 



U. S. Dept. of Agriculture, Bulletin 563. 



