132 MILK AND DAIRY PRODUCTS PART 



view is particularly well seen if, following Storch's example, the 

 dark-field illumination is used. This is obtained by placing a 

 small disc below the condenser of the microscope, and so cutting 

 off the central rays, so that the preparation is only illuminated 

 by the peripheral rays. A diaphragm is screwed into the 

 objective. The drops of liquid now appear as small, highly 

 refractive globules against a completely dark background of 

 butter fat. 1 



Storch has shown that butter which has a dull, opaque 

 appearance contains a very large number of extremely finely 



FIG. 54. 1 : 400. Barthel photo. Microphotograph of " Thick " Butter. 



divided drops of liquid (see Fig. 54) whereas clear, bright butter 

 (Fig. 55) has within it a much smaller number of these minute 

 drops, the size of which, however, is larger than in the first case. 

 Butter on the surface of which drops of brine form on keeping 

 contains not only these small, isolated drops, but also very large 

 ones, often of irregular shape, and they are formed by the 

 running together of the small drops. Although it appears 

 from microphotographs as though the butter fat forms a homo- 

 geneous mass, this is not really the case. Storch has proved that 

 the fat globules of the milk retain their original shape even 

 after being churned into butter. In order to see the outline of 



1 Figs. 54 and 55 show such dark -field photographs. 



