184 UNIVERSITY (OF WISCONSIN STUDIES 
able importance have been observed. Ayers and Johnson? 
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 
p2r ¢. ¢., while 91 samples examined during the winter months 
ranged from 13,000 to 114,000,000 and averaged 10,388,222 
per ¢. ¢. 
The great bulk of the ice cream manufactured in the U. 8. 
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* has found that 
the bacterial content of ice cream other than vanilla is es- 
sentially the same as that of vanilla and this finding is sub- 
siantiated by data published by various laboratories. Water 
sherbets, on the contrary, contain comparatively small num- 
bers of bacteria; the Iowa Agricultural Experiment Station’ 
found in 17 samples that the counts ranged from 6 to 7,800 
per @. ¢. with no 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® 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® have more re- 
2U. 8S. Dept. of Agriculture, Bulletin 303. 
4 Unpublished data. 
5 Bulletin 134, p, 298. 
°U. S. Dept. of Agriculture, Bulletin 563. 
