Journal of Agricultural Research 
Vol. II, No. 3 
186 
in the pasteurized-inilk cheese the Bacterium casei group common to 
both of these types of cheese is responsible for the biting taste which is 
characteristic of the well-ripened cheese. 
Jensen has explained the action of the Bacterium casei group in pro¬ 
ducing amino acids as due to an “endoerepsin” set free by the dead 
cells rather than to the activity of the living bacteria, because he found 
the greatest amount of amino acids formed after the bacteria were for 
the most part dead (Jensen, 1912). 
Whatever may be the condition in the Emmenthaler cheese which Jen¬ 
sen studied, this explanation for the activity of the Bacterium casei group 
in Cheddar cheese is not necessary. It appears to be certain that the living 
bacteria were active throughout the ripening period in this type of cheese. 
Cheese No. 17 R (Table IX) and cheese No. 307 C (Table XV) both demon¬ 
strated this fact. In cheese No. 17 R there were 10,000,000 living bacteria 
of the B . casei group per gram of cheese when 8 months old; cheese No. 307 
C contained a similar number at 7 months. These bacteria did not 
appear to be living in a latent condition, for all three varieties of B , casei 
readily grew upon an agar made with only an extract of the cheese for a 
food substance. Every time an analysis was made of cheese No. 17 R 
such an agar was prepared on the day the analysis was made, using for 
the cheese agar a part of the plug which served for bacteriological analysis. 
Thus, the cheese organisms were submitted for development upon the 
same food substance which served them in the cheese itself. 
The result of the bacterial count upon this cheese agar was only slightly 
smaller than the total count upon the casein agar. Every variety of 
cheese organisms grew upon this medium. On the eighty-ninth day, 
when 32,000,000 organisms per gram of cheese developed colonies on the 
casein agar and of the 10 colonies isolated none belonged to the Bacterium 
casei group, 20,000,000 colonies developed upon the cheese agar, of which 
20 per cent, or 4,000,000 bacteria per gram, belonged to the B . casei group. 
The flask dilutions on that same date showed 1,000,000 bacteria of this 
group per gram of cheese. Thus, it is shown that several millions of 
living organisms of the B . casei group are present in a normal Cheddar 
cheese 3 months of age, and the cheese itself provides suitable food for 
development. It is most probable that under these conditions the living 
bacteria are active in the cheese. 
INFLUENCE OF BACTERIUM CASEI IN STARTERS FOR PASTEURIZED- 
MILK CHEESE 
Many experimental pasteurized-milk cheeses have been made with pure- 
culture starters, to determine their influence upon the production of flavor. 
In the first series some variety of Bacterium casei was added to a num¬ 
ber of the cheeses, together with the B . lactis acidi. When variety "a” 
was added, there was a tendency for the cheese to become f ‘acid injured * *— 
strongly acid, friable, and opaque. The use of variety “b” as a starter 
