In animal hairs the imbria&ted^caLe^jplthe cuticle_are very large, and
marked with step-like or" wavy projections. The medulla of J^e_hurnan hair
is narrow and in some Ceases absent ; while in the animal hair the medulla
is conspicuous^ and, when seen under low power, is found to contain round
or^ojval .and prominent, cuboidal epithelial cells. The cortex forms the bulk
of the shaft in the. human hair, and is, as a rule, four to ten times as broad
as the medulla ; while in that of the lower animals the cortex is rarely more
than twice as broad as the medulla, and often presents only a thin shell
enclosing the medullary cells.
Before giving a decisive opinion it is advisable to compare under a
microscope the specimen of the hair sent for medical examination with a
sample taken from the same part of the individual or animal whence it is
alleged to have been derived.
Fibres. — The fibres whick are most ^mmpnly ^ased in the manufacture
of clothing are those of cottoi^ linefi, ju^sil^nd^td^ Of these the first
three are of vegetable origin ancTffie latter two^feof animal origin.
When examined under a microscope, cotton fibres are seen as
^hciyij^^ edges, and T^^ly_ppmted apicesi In
a transverse section they exhibit a flaHene37^SH°rni3 dumb-bell shaped or
irregular outline and an elongated lumen, ^n^ji^fibries^aa^e^derived from
flax, and_consist of thick walls with jointed^markings at unequal distances
and ~ sharply poinfi§cTlipices. Transverse sections are uniformly_pg]ygonal,
and show a narrow lumen. Jute fibresjare smooth^^nd_do_not show trans-
verse lines or longitudinal .mar&ings. ~~TKe cell cavity is not uniform
throughout the length of the fibres and may disappear in some places. The
ends are mostly blunt or rounded. Silk fibres are structureless and non-
cellular when examined microscopically. They are externally smooth and
finely striated. WooUen, jfib:res_^_e^fine^c^^ and consist
of cpaaedulla oLpolyiiBdral or- rounded cells, a -cortex of spindle-shaped fibres
with nuclei and an epithelium of imbricated scales, the free edges of which
point towards the apices of the fibres and give rise to characteristic trans-
verse markings on the surface.
A rough physical test to distinguish between vegetable and animal fibres
is to burn them in a flame. Vegetable fibres burn very readily without
producing any disagreeable odour, while animal fibres burn with some
difficulty and emit a disagreeable odour resembling that of burning feathers.
Vegetable fibres burn off sharply at the end, whereas animal fibres fuse to
a rounded, bead-like end.
The following chemical tests may be employed for determining the
source of the fibres : —
^ 1- Cold concentrated sulphuric acid ,(66 ...percent) dissjolms.- silk- and
'cotton fibres, buF3^_^
2. Warm hydrochloric acid readily dissolves silk fibres, whereas it has
no action on the fibres of wool, cotton, linen and jute.
3. A five per cent solution of potassium or sodium hydroxide dissolves
animal fibres but not vegetable fibres. *s-
4. Thymol* and sulphuric acid give a violet colour to cotton, linen and
jute fibres, but no colour to silk or woollen "fibres.
5. Sgdiurn nitroprusside (2 grammes in 100 cc. of water) produces a
t^^ but not with cotton, linen, jute or silk fibres.
6. One millilitre of water, two drops of a 15 per cent alcoholic solution
of alphanaphthol and one millilitre of concentrated sulphuric acid are added
to about 0.01 gramme of a fibre placed in a test tube. The mixture, when
shaken, assumes a deep violet colour if the fibre is of vegetable origin, but