276 GENERAL MICROBIOLOGY 



C. MACROSCOPIC SEDIMENT TEST 



Method. 1. Put a cotton disk in place in the pneu- 

 matic sediment tester, heat the sediment tester and clean 

 empty milk bottle in steam thirty minutes, and allow to 

 cool. 



2. Attach the sediment tester to the top of the milk 

 bottle containing the sample of milk, using " aseptic " 

 precautions, and invert the whole apparatus over the mouth 

 of the sterile empty milk bottle. 



3. Pump the contents of the upper bottle into the lower 

 bottle by means of the rubber bulb. The milk is forced 

 through the cotton disk and leaves its larger particles of 

 insoluble dirt on the cotton. 



4. Note the quality of the milk tested by this method. 

 Is there any interrelationship between microscopic sedi- 

 ment test, and the macroscopic sediment test? , , 



5. What does the presence of visible dirt on the cotton 

 indicate? Is this sediment te^t an argument for straining 

 milk before it goes to the consumer? Is it an argument 

 for running milk through a milk clarifier before putting it 

 on the market? 



6. Immediately after straining, plate the milk in lit- 

 mus lactose agar, using dilutions 1 : 100, 1 : 10,000 and 

 1 : 1,000,000 as before. 



7. Incubate, the plates for five days at 25 C. and count, 

 estimating total average number and proportions of types 

 as in A. 



8. Compare the counts with those of A, also the propor- 

 tions of the various types. 



Note. This method was formerly used for obtaining an estimate 

 microscopically of the numbers of bacteria in milk. It presents 

 difficulties, however, which lead to many technical errors and there- 

 fore it cannot be relied upon to give uniform results. The method is 

 valuable, however, for determining something of the sanitary quality 

 of the milk, 



