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 zyy_ millimeter, or s¢y7 of an 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-millimeters 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 million 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 the 
smaller globules. But this is by some investigators considered 
to be a matter of conjecture. Most authorities now believe 
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 which 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, Vol. I. 
