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former are quite resistant to that agent. Animal fibres are mainly restricted to the
making of textiles. The number used is relatively small and may be divided into
two kinds. One is the epidermal hair of animals of which the wool from sheep is
the most important. Particularly characteristic of animal hairs are the tiny scales
which completely surround the shaft. These are embedded in an epidermal layer
over a cortex or fibre layer. A medulla or pithy center may or may not be present*

figure 2. Three types of fibres, adapted from photomicrographs at 100 diameters, in
Chemistry of Pulp and Paper Making^ by Edwin Sutermeister, 2d ed. (New York: John
Wiley and Sons, Inc., 1929),, Plates I, 1, and 6: at a a drawing showing a group of cotton
fibres; at b a group of linen fibres; and at c a group of paper mulberry fibres.
Animal hairs are very long as compared with most vegetable fibres. The identi-
fication of a fibre as a hair is simple because of the scales, but the identification of
hair as to its source is rather difficult. Among the hairs of textile importance there
are slight individual differences which allow at least a partial identification of the
source; the quantitative measurements of diameter and scale size are of great aid
in verification of qualitative observations as to the shape of scale and kind of
medulla. Silk is another kind of animal fibre. True silk is the continuous filament
that forms the cocoon of the Bombyx mori, the worm that feeds on the leaves of
the mulberry tree. The silk fibre is, in reality, a double fibre bound together with
sericin or silk glue. The two individual fibres are separated by boiling in soap and
water which dissolves the sericin. Tussah or wild silk is the secretion of wild silk
worms; it is difficult to decolorize and, hence, is usually dyed a dark color.
The vegetable fibres are numerous and diversified in characteristics. They are
colloidal bodies made from cellulose and derivatives of cellulose. In all the
higher forms of plant life the living cells consist essentially of protoplasm sur-