Frost-Bacteriological Control of Public Milk Supplies. 1355 
yet the pasteurized milk may show a count of 100,000 per cubic 
centimeter. When pasteurized milk contains only 10,000 bac¬ 
teria per cubic centimeter the percentage reduction may only 
have been 95 per cent. It is often impossible to obtain a 99 per 
cent, reduction when, a good quality of milk is pasteurized, 
therefore, regulations which require a 99 per cent, re¬ 
duction of bacteria during pasteurization are of no value.’* 
Following these theoretical considerations it will be of interest 
to notice the results which were obtained in this study. Before 
doing so, however, it will be desirable to explain that while the 
forms under discussion are headed spores, that some and perhaps 
at times many of the forms thus grouped are not spore-forming. 
A better term than “spores”, to use in this connection, would 
be “heat-resisting forms.” Occasional attempts to determine 
the presence of spores in cultures from plates obtained directly 
from the milk have showed that some ten of the twelve or more 
forms examined were, however, spore-bearing. At first it was 
considered necessary only to heat a few c. c. of the milk in test 
tubes to 80° C. for 10 minutes. Lest, however, a scum! should be 
formed, which Theobald Smith, and Russell and Hastings, and 
others have shorn) will protect the contained bacteria from the 
usual effects of the heat, dilutions of the milk, 1-100, were used. 
One cc. of this heated dilution was then plated in duplicate and 
allowed to grow from 6 to 8 days at room temperature. This 
long period of incubation having been found necessary. 
Turning now to Table IX. it is seen that the raw material milks 
contain a considerable number of heat-resisting forms. In a 
general way the higher the bacterial content the higher the aver¬ 
age spore count, and vice versa. If there is a low bacterial 
count comparatively few highly resistant forms will be formed. 
There are. however, some glaring exceptions for which there is 
no data to furnish an explanation. 
The inspected milks have a comparatively large number of 
heat-resisting forms, larger even on the average than the raw 
market milks, the only explanation of which seems to be that 
these milks have in all probability been kept cooler, and that the 
figures obtained represent the original spore content more nearly 
than those of the market milk do, where there has presumably 
been more opportunity for the spores to germinate. 
The certified milks invariably have a very low spore content. 
