COMPOSITION OF MILK AND CREAM 



45'. 



over i62 u F. About i/ii part of the proteids of milk consists of 

 lactalbumin. 



If milk is kept a long while, the cream (mostly fat) rises to 

 the top ; the casein settles as another white layer to the bottom of the 

 vessel, while in between these is seen, a third clear layer (serum) 

 consisting of water, in which remain dissolved the mineral matter, 

 sugar, globulin and albumin (Fig. 2). 



The fat in milk occurs as the most minute, microscopic globules 

 which float through the milk and, on account of their buoyancy, rise 

 more or less quickly to the surface and there form cream. These 

 minute droplets of fat are apparently surrounded by a wonderfully 

 thin pellicle or covering which has been thought to consist of a layer 

 of casein adhering by capillary attraction. This surrounding mem- 

 brane does not exist, according to recent research, milk being a 

 natural emulsion. The fat globules vary greatly in size, some being 

 six times the diameter of others. They average about 1-5,000 of 

 an inch in diameter, and one drop of milk no larger than a pinhead 

 may contain 1,500,000 fat globules. The difference in the size of" 

 the fat globules in different breeds of cows and in human milk is. 

 shown by Gilbert's table. A micron = 1/25,000 of an inch. 



Size of Fat Globules in Different Kinds of Milk. 



The larger globules of fat are most buoyant and rise to the 

 surface; only the smallest remain in skim milk. The fat globules 

 are larger in some breeds of animals, particularly the Jerseys, and 

 the cream therefore rises more rapidly and completely. The size of 

 fat globules in mixed milk varies from 2 to 30 microns. As the 

 lactation period advances the globules diminish 2 or 3 times in size 

 and increase 2 or 3 times in number. While there are breed dif- 



