Fibres obtained from the cocoons spun by the larvae Bombyx mori Linn., belonging to family Bombycidae/Moraceae.
SILK
Biological Source
Fibres obtained from the cocoons spun by the larvae Bombyx mori Linn., belonging to family Bombycidae/Moraceae.
Geographical Source
China, France, Iran, Italy, Japan, and India.
History
It is native to northern China and Persia presently known as
Iran. Bombyx mori is a member of a
small family of about 300 moth species.
The credit for the discovery of silkworm’s silk goes to an
ancient empress in China, who while walking around accidentally, noticed the
worms. When she touched it with her fingers, the silk came out and surrounded
her finger. When the full silk had come out, she saw the small cocoon inside
it; which was responsible for the formation of silk. It is even said that the
Chinese princess smuggled eggs to Japan by hiding them in her hair and thus
they began their love affair with silk. Due to its captivity for thousands of
years, Bombyx mori is fully
domesticated and cannot survive without the support of mankind.
The silkworm is the larva of a moth. Larvae are monophagous
which takes only mulberry leaves as its diet. The cocoon is made of a single
continuous thread of raw silk from 300 to 900 metre long. The fibres are very
fine and lustrous, about l/2500th of an inch in diameter. One pound of silt can
be made from about 2,000 to 3,000 cocoons, and it is estimated that almost 70
million pound of raw silk are produced each year. It requires about 1 billion
pounds of mulberry leaves to produced 7 million pounds of raw silk and one pound
of silk is almost equivalent to 1,000 miles of filament.
Preparation
One gram of silk-worm egg consists of around 15,000 eggs
which are kept at 0°C to overcome the immature development. The silkworms eat
mulberry leaves day and night and they grow very fast. When the colour of their
heads changes darker, it indicates that the time for them to moult has come. It
require almost a month time for its development into full size. During this
period it takes four moulds and their body turns slightly yellow reaching a
size of 4 cm long. The silk-worm finally eats a meal which is about twenty to
twenty five times its weight of leaves and attains a size of 9 cm length and 10
mm thick. The skin becomes tight and all these symptoms indicate that it is
going to cover itself with a silky cocoon. The process of spinning cocoon
continues for almost three days. After 7–8 days, the larvae changes into
chrysalides, and the cocoons are collected by throwing them into boiling water,
this kills the silkworms and also makes the cocoons easier to unravel. If the
caterpillar is left to eat its way out of the cocoon naturally, the threads
will be cut short and the silk will be useless. The cocoons are kept in hike
warm water to remove the gum. Since all the eggs hatch almost the same time,
the cocoons also be collected together and treated at the same period. Some
amount of cocoons are retained and allowed to come out for fertilization. The
females lay nearly 500 eggs and these eggs are stored till further requirement
is wanted.
Description
Chemical Constituents
Silk mainly consists of protein known as fibrion. Fibrion is
soluble in warm water and on hydrolysis yields two main amino acids, glycine and
alanine.
Uses
Silk is used pharmaceutically in the preparation of sutures,
sieves, and ligatures. The ‘stiff silkworm’ (dried body in the four to fifth
stage of larva, which dies due to infection of the fungus Beauveria bassiana) is used in the traditional Chinese medicine.
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