in size
from 1/16,000th to 1/25,000th part of an inch, and occasionally they are
much smaller and also much larger.

Fig. 1 is a micro-photograph showing the fat globules in whole milk.
Fig. 2 is a micro-photograph of separated milk, and Fig. 3 a
micro-photograph of cream, all under high magnification (450 diams.);
from these figures the comparative number of fat globules present may be
seen.

[Illustration: FIG. 1.--Micro-photograph of a Drop of
Whole Milk, showing distribution of fat globules.
(Magnified 450 diams.)]

[Illustration: FIG. 2.--Micro-photograph of Separated
Milk, showing the almost complete absence of fat globules
as compared with whole milk. (Magnified 450 diams.)]

[Illustration: FIG. 3.--Micro-photograph of Cream, showing
agglomeration of fat globules. (Magnified 450 diams.)]

Fats distributed through a watery liquid in this finely divided
condition form together what is called an emulsion, in which the
particles of fat are kept apart by surface tension. The specific gravity
of milk fat averages 0.93, and compared with water weighing 10 lbs., a
gallon of fat would weigh 9 lbs. 5 oz. It is thus considerably
lighter than the other constituents, and when milk is left at rest, the
fat globules gradually rise to the top and float there, forming cream.
The difference in specific gravity between cream and milk is taken
advantage of in the mechanical separator, now so much used, and which
makes such a thorough separation between the two. Cream is an article of
the most varied composition, according to the ideas of the person who
produces it, but it ought to contain at least 20 per cent. of butter
fat, and may be made with a much larger percentage if necessary. When
cream is agitated in a particular way, as by churning, the surface
tension of the particles is overcome, and they run together into a mass
which forms butter.

The casein of milk is not held in solution in the ordinary sense, but in
a peculiar state of suspension called the colloidal condition,
practically the whole of it remaining behind when milk is filtered
through clay filters.

It is this state of suspension of the casein which makes milk opaque,
but the opacity is considerably increased by the emulsified fat.

The coagulation of the casein in milk by the addition of rennet has
already been referred to. Acids, either mineral or organic, also
precipitate it in the form of flakes. Skimmed milk is now largely used
for