lobular form and pulpy condition.
Surrounding this central portion or medulla, as it has been called
(see fig. 3), and forming the main bulk of the fibre, there is a
comparatively thick layer of partially flattened cells, which are also
elongated in the direction of the length of the fibre, and outside
this again there is a thinner stratum which may be compared to the
bark of a tree. This outer covering differs materially from the (p. 005)
rest of the fibre in its physical structure, but is, probably, nearly
identical with it, though possibly not entirely so, in chemical
composition. It consists of a series of flattened horny scales, each
being probably an aggregation of many cells. The scales, which have
been compared to the scales of a fish or to slates on a housetop,
overlap each other, the free edges protruding more or less from the
fibre, while the lower or covered edges are embedded and held in the
inner layer of cells. The free edges always point away from the root
of the fibre, just as do the bracts of a fir cone.

When viewing a section of a wool fibre there is, of course, no sharp
line of division between the three portions above described, but the
change from the central spherical cells to the elongated cellular
portion, and from these again to the flattened horny scales, is quite
gradual, so that the separation into zones, though well marked, is
very indefinite in respect of boundaries.

The scaly structure of wool is of great importance in regard to what
is known as felting property. When woollen fabrics are worked in
boiling water, especially in the presence of soap, they shrink in
length and breadth, but become thicker in substance, while there is a
greater amalgamation of the fibres of the fabric together to form a
more compact and dense cloth; this is due to the scaly structure of
the wool fibres enabling them to become entangled and closely united
together. In the manufacture of felt hats this is a property of very
great value.

#Variations in Physical Structure.#--Wool fibres vary somewhat amongst
themselves; fibres from different breeds of sheep, or even from
different parts of the same animal, vary greatly, not only in
thickness, length, etc., but also in actual structure. A typical wool
fibre, such as may be obtained a good merino or Southdown fleece, will
possess the typical structure described above, but frequently the type
is departed from to such an extent that the central core of