UNITED STATES DEPARTMENT OF AGRICULTURE 
Washington, D. C. 
BULLETIN No. 303 k 
i 
Contribution from the Bureau of Animal Industry 
A. D. MELVIN, Chief 
PROFESSIONAL PAPER 
.tfJ&'^vSU 
October 29, 1915 
A BACTERIOLOGICAL STUDY OF RETAIL 
ICE CREAM. 
By S. Henry Ayers, Bacteriologist, and William T. Johnson, Jr., Scientific Assistant, 
Dairy Division. 
INTRODUCTION. 
A bacteriological examination of ice cream as the consumer re- 
ceives it from retail sources is, we believe, the first logical step in the 
study of the bacteriology of ice cream. The results obtained from 
the examination of ice cream in this last period of its history will show 
the final bacterial flora. This type of investigation does not show 
where the organisms are introduced, but it will show the number and 
kinds of bacteria present in the cream at the time it is consumed. To 
determine where these organisms are introduced and their signifi- 
cance is another phase of the general problem. 
It is well known that commercial retail ice cream contains large 
numbers of bacteria. This is well illustrated in a summary of the 
results of examination of ice cream in various cities, presented in 
Table 1, taken from a paper by B. W. Hammer. 1 From these figures 
it is evident that the number of bacteria in ice cream throughout the 
country averages extremely high. 
Table 1. — Summary of Hammer's bacterial investigations of ice cream. 
Source. 
Date of 
investi- 
gation. 
Number 
of sam- 
ples ex- 
amined. 
Bacteria 
per cubic centimeter. 
Average. 
Highest. 
Lowest. 
Philadelphia 
1905-06 
1906-07 
1906-07 
1909 
1910 
1911 
1911 
1911 
1911-12 
49 
35 
263 
89 
306 
17,833,031 
23,000,000 
26,612,371 
16,662,134 
15.401,000 
1,800,000 
79, 800, 000 
150,000,000 
365,000,000 
125, 000, 000 
100,000,000 
200,000,000 
8,000,000,000 
39,000,000 
72,000,000 
70, 000 
Boston 
Washington tt 
1,000,000 
137,500 
Chicago 
20, 000 
Do 
20,000 
90,000 
Do 
Milwaukee 
26 
10 
11 
200,000 
Des Moines 
Iowa State College 
19, 920, 000 
19, 775, 000 
4,200,000 
500,000 
1 See biblic 
5020°— Bull. 303—15 1 
)graphy at 
end of pa 
per. 
