226 Journal of Agricultural Research voi. xiii, no. 4 



made a study of mold-ripened cheeses. His observations (6) led him to 

 believe that those two microorganisms were — 



capable of ripening Roquefort cheese without the introduction of other enzyme pro- 

 ducing or flavor producing organisms. 



In the Dairy Division experimental work, when cheese of the Roque- 

 fort type was obtained, the question was raised as to whether the bacterial 

 flora had anything to do with the difficulties which arose; whether cheese 

 made from sheep's milk, according to the Roquefort way in France, 

 differed significantly in its bacterial flora from cheese made in a similar 

 manner from cows' milk in America. Accordingly, a study of the 

 bacterial flora of Roquefort cheese, imported and experimental, was 

 undertaken. 



METHODS OF CHEESE EXAMINATION 



The method of examination was similar to that used in the bacterio- 

 logical analyses of Cheddar cheese (4). Plate cultures were made on infu- 

 sion agar, and for comparison numerous colonies were "fished off" into 

 litmus skim milk. Representative cultures of every type of organism 

 appearing in considerable numbers were saved for detailed study. 



Cultures for study were also obtained by the following method: Milk 

 cultures were inoculated from dilutions of a cheese emulsion, the dilu- 

 tion increasing from tube to tube by a ratio of 10. The dilutions ranged 

 from I to 10 to I to 1,000,000,000. The lower dilutions were inoculated 

 into tubes which had been modified as follows to separate the mold 

 growth from the bacterial growth : Ordinary test tubes were drawn out 

 to form a constriction beginning about 4 cm. from the bottom of the 

 tube and filled with skim milk to about 2 cm. above the top of the con- 

 striction. Since oxygen is required for mold growth, the part of the 

 culture below the constriction was always free from molds. By break- 

 ing the tube at the constriction it was possible to obtain a subculture of 

 bacteria free from molds. As soon as a milk culture in any dilution 

 showed evidence of bacterial growth, it v/as plated out to obtain a pure 

 culture of the predominating organism. Many of the cultures thus 

 obtained duplicated the cultures obtained by the plate method, but 

 sometimes an organism was obtained which would be missed if plate 

 cultures alone were made. 



The pure cultures were studied morphologically and biochemically. 

 The detailed study of the different groups of organisms will be presented 

 in separate papers, for the bacteria of Roquefort cheese are not of types 

 peculiar to that kind of cheese, but are ripening agents common to many 

 other kinds, each species differing in importance in different kinds of 

 cheese, according to the various conditions to which it is subjected. 



