or making carpets, curtains, and heavy plushes,
for which they are very suitable.

CHAPTER XVII

SILK

=Silk.= The silk of commerce is obtained from the cocoons of several
species of insects. These insects resemble strongly the ordinary
caterpillars. At a certain period of its existence the silkworm gives
off a secretion of jelly-like substance. This hardens on exposure to
the air as the worm forces it out and winds it about its body.

[Illustration: MOTH, SILKWORM, AND COCOONS]

It takes about three days for the worm to form the cocoon. After the
cocoon has been formed the silkworm passes from the form of a
caterpillar into a moth which cuts an opening through the cocoon and
flies away. It is very important that the moth should not be allowed
to escape from the cocoon; the mere breaking of the cocoon greatly
decreases the value of the thread. The cocoon is preserved by killing
the chrysalis by heat.

There are a great many varieties of caterpillars, but few of them
secrete a sufficient quantity of silk to render them of commercial
value. The principal species is the mulberry silkworm which produces
most of the silk in commerce. It is cultivated and fed on mulberry
leaves. There are other varieties of silkworms that are not capable of
being cultivated and are called wild silkworms. The silk produced by
the wild worms of China and India is called "tussah" (or "tussur").
The silk is inferior to that produced by the cultivated worms and is
used for making pile fabrics, such as velvet, plush, etc.

The color of the cocoons varies greatly. Most of the European cocoons
are bright yellow, though some are white. The Eastern cocoons, on the
other hand, are mostly white, while a few are yellow. The wild silks
are for the most part ecru color, though some are pale green. The
color, except in the wild silks, is derived from the gum which is
secreted by the worm, and with which the fibers are stuck together.
This gum comprises from 15 to 30 per cent of the weight and is removed
by boiling in soap and water before the silk is dyed. All silks except
the wild silks, after the gum is removed, are from white to cream in
color. The tussah, or wild silks, remain an ecru color.

[Illustration: REELING RAW SILK]

The greatest care has to be exercised throughout in the care of the
moths, eggs, worms, and cocoons--this being the succession of
changes. That is, the moth lays eggs which are collected and kept cool
till the pr