COMPOSITION OF MILK. 7 



siderably, according to breeds, individual cows, and the stage 

 in the lactation period. The globules in the milk from the same 

 cow also vary a great deal. Lloyd found that fat-globules in 

 Jersey milk to be from 8 to 12 micro-millimeters in diameter. 

 Very few were less than 4 micro-millimeters (a micro-milli- 

 meter is Y^Vo millimeter, or gg-^iro of a^n inch). The majority 

 of the fat-globules in milk from Shorthorn cows measured from 

 6 to 8 micro-millimeters in diameter. According to Fleisch- 

 mann, the size of fat-globules varies between 1.6 micro-milli- 

 meters and 10 micro-milhmeters in diameter. A Danish in- 

 vestigator maintains that the diameter of fat-globules is 

 between .0063 and .00014 millimeters, and that 1 cubic centi- 

 meter of milk contains from 2.6 to 11.7 milUon globules. He 

 also asserts that a reflection of the light renders it very difficult 

 to get the proper size of the fat-globules, as the light tends to 

 make the globules appear larger than they are in reality. 



It has been maintained by some that the larger fat-globules 

 contain fats which are different from those contained in tlie 

 smaller globules. But this is by some investigators considered 

 to be a matter of conjecture. Most authorities now belie\'e 

 that there is no difference in the kinds of fat of the different- 

 sized globules, even though some experiments * show that fat 

 composed of larger globules has a finer flavor, and a little more 

 oily appearance. 



From what has been said, it will be seen that the minute- 

 ness of the fat-globules is almost inconceivable. They were 

 first discovered in 1697 by A. von Leeuwenhoek. The minute 

 state of division, or the form of emulsion in wliich they exist 

 in milk, renders it easy to digest when consumed as a food. 



Properties of Fat. — The specific gravity of pure butter-fat 

 at 15° centigrade is .93002. The refractive index of butter- 

 fat at 22° centigrade is on an average 1.459. The melting- 

 point of pure butter-fat, as now determined, varies between 

 32° and 37° centigrade. (90° F. and 99° F.) 



* Gembloux, Belgium, Creamery Jo., London, No. 8, Xo\. I. 



