MILK 



121 



Milk may be described as a uniform suspension of fat globules 

 in an aqueous solution of milk-sugar and casein. The fat globules 

 represent the so-called butter fat of the milk. They are fairly uni- 

 form in size, very uniformly distributed and under ordinary con- 

 ditions do not tend to coalesce or clump. Pasteurization and 

 boiling the milk does cause some of the globules to unite or rather 

 to form aggregates but even in such cases it is possible to recognize 

 the individual globules. 



On mounting a droplet of diluted milk (1-150 to 1-200) on the 

 hemacytometer it will be found that the fat globules soon rise to 



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Fig. 37. — Milk fat globules. Larger field as they appear under the low power of 

 the compound microscope (X 80), globules in the corner circle as they appear under 

 the high power (X 500). — {Hunter, after S. M. Babcock.) 



the top while the heavier particles, such as bacteria and body cells, 

 sink to the bottom of the cell, thus separating these elements auto- 

 matically, and making the counting of globules and bacteria pos- 

 sible in the same mount by simply focusing sharply upon the fat 

 globules or upon the bacteria as may be desired. Some difficulty 

 in making the counts is caused by the fact that the oil globules are 

 out of focus when the ruhngs are in focus, making a constant shift- 

 ing of focus from fat globule to lines and vice versa from lines to fat 

 globule, necessary. Not only is this annoying but it makes accu- 

 rate counting difficult. This difficulty can be overcome by com- 



