Journal of Agricultural Research 
Vol. II, No. 3 
170 
groups of cheese organisms. After many cultures had been submitted 
to these tests it was found that some of the substances had no differential 
value. All of the cultures produced acidity from some of the substances, 
while none of the cultures, or exceedingly few, produced acidity from 
other substances. Moreover, not all of the test substances which proved 
of value in differentiating into varieties the members of the coccus and 
Bacterium lactis acidi groups were equally valuable in the study of the 
B . casei group. 
After a preliminary study of 250 cultures of the cheese organisms on 
the 10 test substances with quantitative determinations of the amount 
of acid produced in the dextrose broth, some of the substances were 
discarded. The study was continued on 5 of the test substances differing 
for the various groups of organisms. 
It now includes approximately 1,000 cultures of cheese organisms iso¬ 
lated from 3 7 different raw-milk cheeses, which represent every stage of 
the ripening period. The test for acid was made after 10 days' incuba¬ 
tion at 37 0 C. Small squares of alkaline litmus paper were placed in the 
cultures. If the color in several cultures of positive and negative reac¬ 
tions is compared this method will detect very slight increases in acidity. 
This method of testing the production of acid with litmus paper differs 
from that of other investigators who have made use of the fermentation 
tests for the classification of bacteria. These investigators have deter¬ 
mined by titration the amount of acid produced in the various broths 
and have considered these data also in their classification. But in any 
work of the nature of the problem under discussion it is important that 
the first stages should be a comprehensive survey of all of the factors 
which may influence the final result rather than a more intensive study 
of any one or more factors which attract attention at first sight. The 
methods which have been followed in the classification of cheese organ¬ 
isms were chosen with the purpose of excluding as much as possible of 
the routine work, which appeared to be of minor importance for this 
study in its present stage, in order to extend it over a larger number of 
samples of cheese. Tor this reason the fermentable substances employed 
for the tests were reduced to the smallest number which appeared ade¬ 
quate for the differentiation. And the titration of the acid produced, 
which in the preliminary study was made in the dextrose broth alone, was 
entirely omitted in the major part of the study. Rogers and Davis 
(1912) have adopted an increase of 1 per cent of normal acid as the division 
between fermentation and nonfermentation. In the case of lactose, salicin, 
sucrose, mannit, and inulin the reddening of alkaline litmus paper gives 
practically the same results as far as the division into fermenters and 
nonfermenters is concerned, for in broths containing these substances 
the reaction is almost always negative or decidedly positive, with the 
development of a considerable acidity. If there is a development of 
acidity in glycerin, the reaction is often slight. The titration of a num- 
