MANUFACTURE OF SILK BY THE SILKWORM.
We now come to the most important of all silk-spinning insects, the
common silkworm, or caterpillar of the mulberry-tree moth. The labours
of this insect were known and appreciated in other parts of the world
long before we had tidings of its existence; so that the peasantry of
other lands were clad in raiment which our kings would have been proud
to wear. “When silk was so scarce in this country that James the First,
while King of Scotland, was forced to beg of the Earl of Mar the loan of
a pair of silk stockings to appear in before the English ambassador,
enforcing his request with the cogent appeal, ‘for ye would not, sure,
that your king should appear as a scrub before strangers;’ nay, long
before this period, even prior to the time that silk was valued at its
weight in gold at Rome, and the Emperor Aurelian refused his empress a
robe of silk because of its dearness, the Chinese peasantry in some of
the provinces, millions in number, were clothed with this material; and
for some thousand years to the present time, it has been both there and
in India (where a class whose occupation was to attend silkworms appears
to have existed from time immemorial, being mentioned in the oldest
Sanscrit books,) one of the chief objects of cultivation and
manufacture. You will admit, therefore, that when nature
——Set to work millions of spinning worms,
That in their green shops weave the smooth-haired silk
To deck her sons,
she was conferring upon them a benefit scarcely inferior to that
consequent upon the gift of wool to the fleecy race, or a fibrous rind
to the flax or hemp plants; and that mankind is not under much less
obligation to Pamphila, who, according to Aristotle, was the discoverer
of the art of unwinding and weaving silk, than to the inventors of the
spinning of those products.”
[Illustration:
EGGS AND SILKWORMS IN THE FIRST AGE.
]
It is so common an amusement with young persons in this country to
procure the eggs of silkworms, rear the insects, and watch their changes
that numbers are acquainted with the growth, habits, and manner of
spinning of these interesting creatures. Perhaps a sheet of paper is
given to a little boy or girl, on which are a number of small specks, no
bigger than pins’ heads: these specks, the child is told, are silkworms’
eggs, and if he keeps them dry during winter, and then places them in a
sunny window in spring, he will get a number of caterpillars from them.
Taking care to do this, the child is delighted some fine morning to see
a few little dark coloured worms crawling about the paper, while others
are just issuing from the eggs. Perhaps a difficulty now arises about
their food. In warm countries the leaves of the mulberry-tree are ready
for the insects as soon as they are hatched; but in England, unless the
eggs are purposely kept back, by putting them in a cold place, the
caterpillars come out before the mulberry-tree has put forth its leaves.
A few tender leaves of the lettuce are therefore spread lightly over the
young caterpillars, and upon these they mount, and at last begin to
feed, after searching in vain for their natural food. But the worms do
not thrive on this diet, and it is much better so to manage the eggs
that they may be hatched when the young leaves of the mulberry are just
opening. These form the best possible food in that tender state, and in
order to economise it, the leaves should be cut in small pieces; because
the caterpillars feed only on the edges, and thus great part of a leaf,
when given to them whole, is entirely wasted.
[Illustration:
THE WHITE MULBERRY.
(_Morus alba._)
]
In Italy, where great attention is paid to the cultivation of the
silkworm, the eggs are hatched in a room heated by a stove, and the
young caterpillars are then removed on their mulberry-leaves to a cooler
apartment called the nursery, where they are managed with great care and
skill. Wicker shelves are arranged in the room at convenient distances,
and are lined with paper, on which the worms are placed. Care is taken
to place together only such worms as are hatched at the same time, for
without this precaution the treatment, with respect to food, could not
be regulated, and the moultings would not take place at the same time.
Great care is also taken to secure the worms from rats and mice, as well
as from certain insect enemies.
Silkworms are so little disposed to wander away from their food that
open trays are sufficient to secure them: but unless great cleanliness
is observed in their management, and frequent change of food given, a
sickly smell is observed, and the caterpillars languish and die in great
numbers. Supposing the young brood goes on well, and is properly
attended by the child whom we have supposed to undertake the charge,
there will be about five or six days’ feeding, and then the worms will
begin to sicken for their first moult, or casting the skin. Silkworms
have four of these moults, at each of which they appear to suffer pain
or inconvenience; they also entirely leave off eating for two or three
days. The caterpillars at that time raise the fore part of their bodies,
and show tokens of uneasiness. They have grown rapidly, and their skins,
not having grown in proportion, now appear to press and inconvenience
them; but after two or three days fasting, they become thinner and are
able gradually to rid themselves of their skin. It is now that their
owner may see the use they begin to make of their silk. By watching them
closely he sees each caterpillar throw out a number of very fine silken
lines, by which it fastens the skin to one spot. Having done this, it is
able to creep out, without dragging the skin about after it, as would
otherwise be the case. In this operation the whole covering of the body,
including that of the feet, of the jaws and teeth, is cast off; but it
sometimes happens that the animal cannot entirely cast its skin, a
portion of it breaking and remaining attached to the extremity of the
body. As the animal increases rapidly in size, this portion of the old
skin compresses its body tightly, causing inflammation and much
suffering, which usually ends in death.
Worms that have newly moulted are readily distinguished by their pale
colour, and the wrinkled appearance of the new skin. Soon after moulting
they recover health and vigour, and feed with increased appetite. To
keep them in health they must be fed with great regularity, and not
crowded together in their trays. In the course of five days the rapid
growth of the insect causes the wrinkles to disappear from the skin; it
is now half an inch in length; a second sickness, and a second moulting,
prepare it for increase of growth; it casts its skin as before, and
feeds without intermission during another five days, during which time
it attains a length of three quarters of an inch. It then falls sick and
moults a third time. It again feeds during five days, after which it
casts its skin for the fourth and last time in the caterpillar state.
[Illustration:
PROGRESSIVE GROWTH OF THE SILKWORM.
]
It is now about one and a half or two inches in length, and devours its
food most voraciously, increasing rapidly in size during ten days. When
the worms are fed a slight hissing noise is heard similar to that of
green wood burning. According to some writers this noise proceeds from
the action of the jaws, but others attribute it solely to the action of
the feet, which are continually moving until the worms have fastened to
their food, when the noise ceases. In a large nursery of silkworms this
noise sounds like a soft shower of rain.
[Illustration:
SILKWORM ON MULBERRY-LEAF.
]
When the caterpillar has attained its full growth, it is a very
different creature from the little black worm which first issued from
the egg, being from two and a half to three inches in length, and its
body consisting of twelve membranous rings, which contract and elongate
as the animal moves. It is furnished with sixteen legs, in pairs: three
pairs in front, under the first three rings, are covered with a shelly
or scaly substance; the other five pairs, called holders, are furnished
with little hooks, which assist the insect in climbing. The head is
covered with a scaly substance similar to the covering of the fore legs.
The mandibles are of great strength, and indented like the teeth of a
saw. Beneath the jaw are two small openings, through which the insect
draws its silken lines. The substance of which the silk is composed is a
fine yellow transparent gum, secreted in two slender vessels, “which are
wound, as it were, on two spindles in the stomach; if unfolded, these
vessels would be about ten inches in length.” The insect breathes by
means of eighteen holes or spiracles, distributed along the body, nine
on each side. On each side of the head, near the mouth, are seven small
eyes; the two specks higher up on the head, which are generally mistaken
for eyes, are only parts of the skull.
[Illustration:
FULL GROWN SILKWORM.
]
When the silkworm is ready to spin, it gets upon the leaves without
eating them, rears its head as if in search of something, or crawls to
the edges of the tray and moves slowly along; its rings draw in, and its
greenish colour changes to a deep golden hue; its skin becomes wrinkled
about the neck, and its body feels like soft dough, and on taking it in
the hand, and looking through it, the whole body has assumed the
transparency of a ripe yellow plum. When this is observed, the owner of
the insects puts each singly into a little cone of white paper, which he
pins to the wall or elsewhere, so that the creature may be undisturbed
at its work. But in the nurseries abroad little bushes are set up on the
wicker shelves, and the insects mount them and form their cocoons among
the twigs.
Supposing the worm to be left to itself on the tray, without either of
these precautions, it at last selects some corner or hollow place which
will conveniently hold the cocoon it is about to spin, and begins by
throwing out a number of irregular threads, which are intended to
support its nest. Upon these it forms, during the first day, a loose
structure of floss silk of an oval shape, within which, during the next
three days, it winds the firm, hard, yellow ball, remaining, of course,
all the time within it. In this operation the insect does not greatly
change the position of the hinder part of its body, but continues
drawing its thread from various points and attaching it to others, so
that after a time the body becomes to a great extent enclosed by the
thread. “The work is then continued from one thread to another, the
silkworm moving its head and spinning in a zigzag way, bending the fore
part of the body back to spin in all directions within reach, and
shifting the body only to cover with silk the part which was beneath it.
As the silkworm spins its web by thus bending the fore part of the body
back, and moves the hinder part of the body in such a way only as to
enable it to reach the farther back with the fore part, it follows that
it encloses itself in a cocoon much shorter than its own body, for soon
after the beginning the whole is continued with the body in a bent
position. From the foregoing account it appears that with the most
simple instinctive principles all the ends necessary are gained. If the
silkworm shifted its position much at the beginning of the work, it
could never enclose itself in a cocoon; but by its mode of proceeding,
as above explained, it encloses itself in a cocoon which only consumes
as much silk as is necessary to hold the chrysalis.”
[Illustration:
THE COCOON.
(_A portion of the floss silk has been removed._)
]
The use of the cocoon, in the natural state of the insect, is to afford
a warm nest, where, secure from the inclemencies of the season, and the
attacks of enemies, it may undergo its final changes. The cocoon is made
water-tight by an internal lining of gum, and the silken thread of which
the ball is made is also smeared with a similar gum, which hardens in
the air.
[Illustration:
THE CHRYSALIS.
]
[Illustration:
GIRL WINDING SILK.
]
While the worm is spinning its cocoon it takes no food, and as it is
continually emitting silk, its body gradually diminishes to less than
half its original length. When its labour is completed it rests awhile,
and then once more throws off its skin; but it is no longer a
caterpillar; its form is changed into a chrysalis, or aurelia, with a
smooth brown skin, and pointed at one end. A few days after the insect
has finished spinning, the cocoons will be ready to be unwound. Our
amateur silkworm cultivator then takes the cocoons out of the paper
cones and separates the outer floss silk. He then throws several cocoons
into a glass of water slightly warm, to make them more easy to unwind,
and having found the ends, proceeds to wind the silk on a reel, or he
gives the task to a sister’s gentler hands, while he prepares a little
box of bran, in readiness to put the poor exposed chrysalis the moment
it is released from the cocoon. As the winding proceeds, the cocoons
become thinner and thinner until the insects within are visible. The
chrysalis, though covered with a horny skin, and apparently without much
sensation, shows very plainly that it is sensible of the rough treatment
it is receiving, as the cocoon is tossed about in the water by the
motion of the reel. It rapidly moves the rings of its tail, which is
doubtless a sign of uneasiness or pain. When nearly all the silk is
wound off, there still remains a transparent film like silver paper,
which is torn open to let out the chrysalis. The latter is immediately
buried in bran, where it remains very quietly for a week or two, then
changes into a cream coloured moth, lays its eggs, and dies. This is the
common domestic treatment when silkworms are kept for amusement, but in
a commercial establishment such as those of Italy, they are very
differently treated.
[Illustration:
FEMALE SILKWORM MOTH AND EGGS.
]
The cocoons are collected in large quantities, separated and sorted
according to their quality, about one-sixtieth part being saved for the
production of eggs, after which the life of the chrysalis is destroyed
in all the rest. This is done in hot countries by exposure to the sun;
but in more temperate climes by artificial heat, such as that of an oven
after the bread has been withdrawn. Before the cocoons can be reeled
they must be separated from the floss, which is done by opening the
floss covering at one end and pushing out the cocoon. Care is taken in
reeling to use cocoons of one quality, as different qualities require a
different treatment.
The natural gum of the cocoons is first softened in warm water, kept at
the proper temperature, either by a charcoal fire or by a steam pipe.
After remaining in this for a few minutes, the reeler (generally a
woman) gently stirs up or brushes the cocoons with a short birch rod,
and to this the loose threads of the cocoons adhere, and are thus drawn
out of the water: they are then taken commonly four or five together,
twisted with the fingers into one thread, and passed through a metal
loop, to get rid of dirt and impurities: the thread then passes on to
the reel, which is so constructed as to have a slight lateral motion, so
that the thread of one revolution does not overlay the other; for if it
did so, the threads would be glued together before the gum had had time
to harden by exposure to the air. The threads of the four or five
cocoons are thus united into one strong and smooth thread. Sometimes as
many as thirty cocoons are united into one thread, and it is difficult
to wind more. As often as a thread of any single cocoon breaks or comes
to an end, the attendant supplies its place by a new one, so that by
continually keeping up the same number the united thread may be wound to
any length: these joinings are not made by a knot, but the new end is
simply laid on the compound thread, to which it adheres by its gum; and
as the threads are finer near their termination than at the
commencement, it is necessary for the reeler to add other cocoons before
the first set is quite exhausted; so that the compound thread may be of
uniform thickness. The filaments of three fresh cocoons, added to two
half-wound ones, make a thread about equal to that from four fresh
cocoons. The cocoons are not entirely wound off, but the husk containing
the chrysalis is used together with the floss silk under the name of
waste. Improved methods of reeling have been introduced on the
continent, but they are similar in principle to the above.
Eleven or twelve pounds of cocoons yield about one pound of reeled silk;
and as from 240 to 250 cocoons weigh a pound, the number of cocoons
required to produce a pound of silk may be estimated at 2,817½. The
length of filament yielded by a single cocoon is 300 yards, but some
have yielded as much as 625 yards.
The reeled silk is made up into hanks for sale or use. The form and
contents, as well as quality, of these hanks, differ greatly, as will be
seen by the following wood-cuts.
[Illustration:
HANKS FROM ITALY.
]
[Illustration:
BOOK OF SILK FROM CHINA.
]
[Illustration:
SLIP FROM BENGAL.
]
We may aptly conclude our account of this most industrious
silk-manufacturer in the words of the Rev. Samuel Pullein, M.A., who, so
long ago as 1758, wrote an Essay on the Culture of Silk, in which the
following passage occurs:—
“There is scarce anything among the various wonders which the animal
creation affords more admirable than the variety of changes which the
silkworm undergoes; but the curious texture of that silken covering with
which it surrounds itself when it becomes a moth, and arrives at the
perfection of its animal life, vastly surpasses what is made by other
animals of this class. All the caterpillar kind do indeed undergo
changes like those of the silkworm, and the beauty of many of them in
their butterfly state greatly exceeds it; but the covering which they
put on before this change into a fly is poor and mean, when compared to
that golden tissue in which the silkworm wraps itself. They indeed come
forth in variety of colours, their wings bedropped with gold and
scarlet, yet are they but the beings of a summer’s day; both their life
and beauty quickly vanish, and they leave no remembrance after them; but
the silkworm leaves behind it such beautiful, such beneficial monuments,
as at once record both the wisdom of their Creator, and His bounty to
man.”
On the importance of the silk itself, Kirby and Spence have the
following remarks:—
“To estimate justly the importance of this article, it is not sufficient
to view it as an appendage of luxury unrivalled for richness, lustre,
and beauty, and without which courts would lose half their splendour; we
must consider it what it actually is, as the staple article of
cultivation in many large provinces in the south of Europe, amongst the
inhabitants of which the prospect of a deficient crop causes as great
alarm as a scanty harvest of grain with us; and, after giving employment
to tens of thousands in its first production and transportation, as
furnishing subsistence to hundreds of thousands more in its final
manufacture, and thus becoming one of the most important wheels that
give circulation to national wealth.”
[Illustration: THE GEOMETRIC SPIDER]