Journal of Agricultural Research 
Vol. II, No. 3 
168 
of the sugar in the cheese by B , laciis acidi . Their continued persistence 
in large numbers must be due to continued growth for a considerable 
period or else to their greater resistance to the environment. But little 
definite information was presented in the bulletin mentioned concerning 
the occurrence of coccus forms, because of the confusion then existing in 
the differentiation of some varieties of this group from the B. lactis acidi 
group. 
It was recognized that we were not dealing with specific organisms but 
rather with great groups. In making cheese of the Cheddar type from 
pasteurized milk it was found that the typical flavor did not develop. 
The milk, after pasteurization, always contained organisms of the Bacteri¬ 
um lactis acidi group, of the B . casei group, and coccus forms, and there was 
added to the milk a starter containing an organism of the B. lactis acidi 
group. In order to obtain a more complete knowledge concerning the 
biological factors present in Cheddar cheese and their r 61 e in the develop¬ 
ment of flavor and possibly to determine the cause of lack of flavor in 
cheese from pasteurized milk, a more detailed study has been made of 
cheese both from raw and from heated milk, with the results as presented 
in this paper. 
In continuation of the above-mentioned work, bacteriological analyses 
of many more cheeses have been made in order to determine more fully 
the distribution of the groups in ripening cheese; and a detailed study of the 
pure cultures obtained has been carried out along new lines with the view 
of correlating the presence of certain types with desirable or undesirable 
flavor production. 
METHODS OF EXAMINATION 
In the previous work the pure cultures were obtained by isolation from 
lactose-agar plate cultures and from dilution cultures made in small 
flasks of sterile milk. These milk cultures were inoculated from a dilu¬ 
tion of a cheese emulsion, the dilution increasing from flask to flask by a 
ratio of io. The above methods have been modified in the present study. 
The dilution cultures were made in milk to which was added i gram of 
peptone, i gram of dextrose, and 200 c. c. of water per liter. This was 
found to be more favorable than plain milk for the development of some 
of the cheese organisms. An effort was made to obtain two pure cultures 
for study from each series of dilution cultures; viz, the predominating 
organism of the combined Bacterium lactis acidi and coccus groups and the 
predominating organism of the B. casei group. The former was obtained 
by plating the culture from the highest dilution of the cheese which 
shows a growth after two days' incubation; the latter was obtained 
after three weeks' incubation. The flask cultures were then titrated 
to determine the highest dilution which contained B . casei . All milk 
cultures which titrated more than 1.15 per cent of acidity were further 
examined for the B, casei group. The long incubation usually killed 
