RELATION OF BACTERIA TO CHEESE 105 



clear zone and the unchanged part of the medium will be noted a 

 zone of increased opacity similar to that produced on the uninocu- 

 lated plate. 



Analysis of cheese. As was pointed out in the discussion 

 on general quantitative methods, it is impossible to determine 

 in any sample the absolute number of bacteria present. In 

 the curd and in the cheese the bacteria are held in place 

 exactly as in a gelatin or agar plate. If growth occurs, colo- 

 nies will result. Thus the distribution of bacteria in cheese 

 is not uniform, but in masses. In the preparation of plate 

 cultures it is essential that as far as possible the masses of 

 bacteria shall be disintegrated. This is done by grinding the 

 cheese with some sharp crystalline substance, as sand, finely 

 ground glass, or sugar. The mixture of cheese and grinding 

 material is suspended in water and well shaken, and plates 

 made therefrom. 



Sampling. If an uncut cheese is to be sampled, a plug 

 must be taken with a cheese trier. The rind over the part 

 to be sampled should be removed with a knife, and a plug 

 taken with a sterile trier and transferred to a large test tube 

 or -flask. The trier may be sterilized by heating in the flame 

 of a gas burner or of an alcohol lamp, or by dipping in alcohol 

 and igniting it. If a cut cheese is to be sampled, an interior 

 piece should be removed, under aseptic conditions, with a knife 

 and placed in a sterile container. The plug .or piece of cheese 

 is split with a sterile instrument, and pieces removed at vari- 

 ous places. A piece of sterile filter paper is placed on the 

 pan of a balance ; on this piece of paper is placed a smaller 

 one, also sterile, on which may be placed the cheese for 

 weighing. Exactly 1 gram is weighed out and transferred 

 to a small porcelain mortar, 10 grams of fine sterile quartz 

 sand are added, and the mixture is ground until the cheese 



