LABORATORY WORK IN DAIRY BACTERIOLOGY 309 



If time should permit, the molds may be further studied. 

 Allow them to grow for several days, when they will show a 

 change in color, due to the formation of spores. The spores may 

 then be taken up on the tip of a platinum needle and planted 

 on other gelatin or agar plates, or upon agar slants, for preserva- 

 tion. The different species of molds are distinguished from 

 each other by their methods of forming spores and, also, by 

 their color. This subject hardly belongs to this book, but any 

 dairy student who is working upon the problems of soft cheese- 

 making should study the molds sufficiently to become familiar 

 with the white mold of the Camembert, the mold of the Roque- 

 fort, and the common blue molds, which are found almost every- 

 where, but are mischievous organisms in the dairy. 



No. 74. Bacteria in Soft Cheeses. From either or both of the 

 cheeses in the last two experiments make litmus gelatin plates. 

 After proper growth, study and determine whether there are 

 any bacteria present except lactic acid germs. In most good 

 cheeses of this type the ripened cheese should contain only lactic 

 acid bacteria. 



*No. 75. Effect of Different Species of Bacteria on Milk. In- 

 oculate a series of sterile milk tubes with a large number of 

 different kinds of bacteria. It is well for this purpose to use 

 all of the species isolated during these experiments, and as 

 many other kinds of bacteria as may be available. Set all of 

 the tubes aside at 70, and at intervals of 24 hours examine 

 each to determine the effect upon the milk of the different 

 species of bacteria. The acidity should be tested by removing 

 a loopful and placing on litmus paper, and special attention 

 should be given to curdling, separation of whey, appearance of 

 gas bubbles, the digestion of the curd and the appearance of 

 odors as a result of the action of the different bacteria. The 

 larger the variety of the different cultures used, the better. 



