8 DAIRYING 



221. Grouping of the Fat Globules. When milk is first drawn 

 from, the udder, the serum is in its most limpid condition, and the 

 fat globules are evenly distributed throughout the serum, in which 

 they move readily. After standing for a time at ordinary temper- 

 atures without immediate cooling, the serum thickens somewhat, 

 and the fat globules group themselves together into clots or clus- 

 ters which rise to the surface slowly. This grouping seems to 

 cause the clusters to drag on their way to the top of the milk. 

 An entirely satisfactory explanation of this grouping into clusters 

 has not as yet been given, but there is some similarity between it 

 and the action of the corpuscles in blood. 



222. Similarity Between Blood and Milk. If blood in the 

 veins is examined with a microscope it will be noticed that the 

 corpuscles appear to be uniformly distributed throughout the 

 liquid, they do not touch one another. This condition of the cor- 

 puscles changes, however, when blood is exposed to the air at 

 ordinary temperatures, the corpuscles then group themselves into 

 clots in very much the same way as the fat globules arrange them- 

 selves in the milk after it stands a while. 



223. Another similarity between the action of the fat globules 

 and the blood corpuscles is the behavior of certain alkalies towards 

 both substances. If caustic soda or potash is added to milk, the 

 grouping of the fat globules is prevented, and the cream rises 

 quickly. These same alkalies prevent the coagulation of blood. 

 It has been further noticed that when blood is immediately cooled 

 to a temperature below 40 degrees F. that it does not coagulate, 

 but remains liquid. A similar action is shown by the fat globules 

 in milk. They remain apart and rise quickly to the surface when 

 the milk is cooled to about 40 degrees F., immediately after draw- 

 ing it from the udder. This cooling must be done at once as a 

 delay of even a few minutes allows the grouping of the fat glob- 

 ules into clusters which rise much more slowly than do the single 

 globules. The substance which entangles the globules is appar- 

 ently heavier than the fat and acts as a load on them. This has 

 been illustrated by certain experiments which have shown that 

 when cream is obtained by "deep setting" of cans of milk in cold 

 water, there may be a loss in the cream if the milk is allowed to 



