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A MICROSCOnC METHOD OF EXAMINING BUTTER FOR 

 MICROORGANISMS. 5.j jj : 



G. L. A. RUEHLE. 



(Published with permission of the Director of the Experiment Station.) 

 In examining a substance for the presence of microorganisms, it is always 



desirable to be able to analyze the material microscopically as well as cul- 

 turally. Without this microscopic check, one is apt to get not only iin entirely 

 erroneous view of the number of microorganisms present and of their condi- 

 tion in the material, but one may also miss a Whole group of organisms 

 entirely, due to the fact that they do not grow on the medium - presented 

 to them. .. l! 



With these facts in view, some work has been started with the purpose 

 of devising and perfecting a technique which will enable us to examine 

 butter microscopically. Since starting the work three other microscopic 

 methods for the examination of butter have been found, described in the 

 literature. They are (1) Roth's method^ for the examination of butter ^6r 

 the Tubercle organism (2) Lohnis' method^ for demonstrating bacteria In 

 butter and (3) Schneider's microscopic method.^ All of these methods are 

 merely for the demonstration of bacteria in butter and all of them depend 

 on the use of the centrifuge and the microscopic examination of the stajned 

 sediment. None of them, it seems, will be useful in determining even the 

 approximate numbers of microorganisms in the butter. For microscopically 

 demonstrating the presence of organisms in butter It is unnecessary to centri- 

 fuge the butter. This has been shown in the present work, incomplete as it 

 Is. All that is necessary is to dissolve some of the butter in a fat solvent in 

 a separatory funnel. After this stands for a short time some of the micro- 

 organisms and particles of casein and some of the moisture of the butter will 

 settle out in the lower part of the funnel and then may be spread on a slide ; 

 stained and examined under the microscope. When so examined, it was 

 found that a large proportion of the bacteria were imbedded in the particles 

 of casein. This would indicate that any cultural method of counting the 

 microorganisms in butter would give counts of bacteria much below the actual 

 number present in the butter. Therefore, it was deemed advisable to attempt to 

 develop a direct microscopic technique for counting the microorganisms in 

 butter similar to the Breed method for counting bacteria and leucocytes In 

 milk. This seemed to be simple enough but as will be shown later, unex- 

 pected difficulties were encountered. 



After some experimentation the following technique was adopted and Is 

 still being studied: . . . 



21st Mich. Acad. Sci. Kept., 1919. 



