he microscope the wool fibres
show a rod-like structure covered with broad scales, the edges of
which project from the body of the fibre, and all point in one
direction.

Fig. 1 shows typical wool fibres as viewed under the microscope; the
sketch shows very well the scales.

The shape of the scales varies in different breeds of wool. The (p. 003)
outer scales enclose inner medullary cells, which often contain
pigment matter. A transversed section of the wool fibre shows the
presence of a large number of cells. Sometimes wool fibres are
occasionally met with which have a peculiar white horny appearance;
these do not felt or dye well. They are known as "kempy" fibres. See
figure 2. The microscope shows that they are largely devoid of
structure, and are formed of very horny, impenetrable tissue, which is
difficult to treat in the milling or dyeing process.

[Illustration: Fig. 2.--Kempy Wool Fibres.]

The curly or twisted character of the fibre is caused by the unequal
contraction of the outer scales, and depends in a great measure upon
the hygroscopic nature of the wool. It may be entirely removed for the
time by wetting the wool in hot water, then drying it in a stretched
condition, or the curl may be artificially induced by unequal drying,
a fact which is turned to practical account in the curling of feathers
and of hair.

The amount of curl in different varieties of wool is very variable,
being as a rule greatest in the finer qualities, and diminishing as
the fibre becomes coarser. The diameter of the wool fibre varies (p. 004)
from 1/2000 to 1/5000 of an inch, and the number of curls from about
30 per cent. In fine wool as little as 1 or 2 per cent. in the thicker
fibres.

Elasticity and strength are properties which, in common with silk,
wool possesses in a greater degree than the vegetable fibres. When
submitted to strain the wool fibre exhibits a remarkable strength, and
when the breaking point is reached the fracture always takes place at
the juncture of two rings of the outer scales, the embedded edges of
the lower layer being pulled out of their seat. The scales themselves
are never broken.

[Illustration: Fig. 3.--Wool Fibre showing Medullary Centre.]

When first formed the cells are more or less of a spherical shape, and
contain a nucleus surrounded by the ultimate photoplasmic substance.
Those cells which constitute the core or central portion of the fibre
retain to some extent this original g