257 
determine the reason for this high frequency, they conducted a study 
on the relative rate of growth of streptococci isolated from milk, 
in milk and cream, and find that there is a much more rapid pro- 
liferation of the organism in cream than in milk. The difference in 
the relative rate of growth is more striking, also, at the temperature 
of the refrigerator (about 12° C.) than at higher temperatures, 
which may account, at least to some extent, for the frequency with 
which this organism occurs in ice cream and also for its overwhelm- 
ing proportion there. 
It was noticed also that the thickening of cream, inoculated with 
pure cultures of streptococci and kept cool, was very marked. Its 
whipping quality greatly increased and the separation of a curd was 
extremely slow, all of which qualities are sought after by the ice- 
cream maker. 
CHANGES IN ICE CREAM DURING STORAGE. 
An important point to be considered in the study of ice cream is 
the change which takes place during the storage thereof. It is quite 
customary at the present time to make a kind of ice cream which is 
intended to be kept a long while and shipped to great distances. 
It is generally supposed that very low temperatures entirely in- 
hibit bacterial growth. That this is not always the case is shown 
by the results of the investigations which are appended. In order 
that some definite knowledge might be obtained of what actually 
takes place respecting the bacterial flora during cold storage two sets 
of investigations were instituted — one in Washington under the 
supervision of Dr. George W. Stiles, and one in Philadelphia under 
the direction of Dr. M. E. Pennington. Doctor Stiles’s report is as 
follows : 
Tlie technique used in the study of ice-cream samples kept in a frozen con- 
dition for about thirty days corresponded very closely to that used in the 
quantitative examination of the ice-cream samples heretofore described. The 
sampling, however, was of necessity somewhat modified. 
From each of four representative dealers twelve 5-cent samples were pur- 
chased, each sample being kept separate in a 5-cent paper carton, as used by 
such dealers. One dealer, however, n,ot having the small cartons at hand 
wrapped the samples each in tissue paper and placed all of them within a new 
pasteboard box. The samples were kept in a cold-storage warehouse where the 
temperature varied from 0° to 10° above 0 F. The graphic chart shows the 
variations in bacterial content of these four groups of samples. 
In addition to making counts of the number of organisms present, each sample 
was tested for gas-producing organisms, and from each a bacillus was isolated 
which belonged to the B. coU group. 
The initial count of sample No. 1 was 16,000,000; of No. 2, 85,000,000; of 
No. 3, 135,000,000, and of No. 4, 53,000,000. The variation from these numbers 
during the keeping of the sample will be noted in the table which follows, as 
24907— Bull. 41—08 17 
