CHAPTER ITHE RAW MATERIAL

Early Sericulture

Silk owes its position as one of the three leading textiles to its qualities of strength, elasticity and beauty—in which respects it surpasses all other fabrics. Its production dates far into antiquity; for centuries China was the seat of the industry, guarding the secret methods and processes with the utmost care. During the sixth and seventh centuries A. D. the secret began to leak out and sericulture gradually found root in the Near East and the Levant, whence it spread to Greece, Italy, France and Spain. Japan also took it up and developed it to a very high point.

Industry in America

Attempts to establish the industry in America have been generally unsuccessful, high costs precluding the possibility of competing with foreign conditions. In addition, the raising of raw silk has been built up principally in countries where there is a system of home industry—a social and industrial system never developed in the United States. However, although America has never been a factor in the producing of the raw material, it has risen to a place of utmost importance in the manufacture of the finished textile. Immense quantities of raw silk are imported from abroad—principally Japan, Italy, and China—and its conversion into the finished products constitutes a most important part of our industry.

Names and Types of Silk Worms

The textile fibre known as silk is a filament secreted by one of two general types of moth larvæ—the cultivated and the wild. The largest proportion is, of course, made up of the former, produced by the worm known as theBombyx mori, while the most common type of wild silk worm is called the Tussah. The nameBombyx moricomes from the name of the family to which the silk worm belongs: theBombycidoe(spinners), andmori, from themorus multicaulisor mulberry tree, on the leaves of which it feeds. The speciesSericaria mori, or silk worm of the mulberry, belongs to the generic class ofLepidopteraor scaly-winged insects.

Bombyx Mori

TheBombyx mori, with which we are chiefly concerned, is divided into other groups according to the cycle of reproduction. The annuals reproduce once a year, and sixty per cent of the silk worms belong tothis class. The bivoltines reproduce twice a year, and the polyvoltines, several times during the year, the first crop being the best.

Full Grown Worms

The study and development of the various phases through which the silk worm passes, leading up to its production of the actual filament, have been a subject of intense research in many parts of the world for a great number of centuries. The present silk worm is nothing more than a highly specialized product of a long train of artificial cultivation.

Stages of Growth

The cultivated silk worm passes through four changes in its life of two months, i.e., egg, larva, chrysalis (or pupa), and adult—a cream-white moth which is about one inch in length. The moths live only a few days, during which mating takes place, and the female lays several hundred eggs; after about six months these eggs hatch into worms. The latter pass through what are known as four “molts,” or shedding of the skin, before the worm matures, spins its cocoon, becomes a chrysalis, and finally emerges as a moth. This, very briefly, is the life history of the silk worm.

Countries Producing Raw Silk

Silk raising, or sericulture, has been a leading industry in Japan and China for a great many years, while the Near East and such countriesas France and Italy have also played a part in the industry—but to a lesser degree. A great deal of this work, particularly in Japan and China, has been carried on as a home industry, but with the growth of modern business methods more and more of the silk raising has come into the hands of companies operating on a highly scientific basis.

Cocoonery

Japanese Supervision

After many years of experience and experimentation the breeding and care of the silk worm has been put on a very technical and closely regulated schedule that minimizes the chances of loss by waste or the spread of disease. In Japan the industry has been encouraged and fostered by the Government; a special division of the administration is devoted to its attention, and numerous organizations and associations conduct experimental stations for research and study. In fact since about the middle of the 19th century everything possible has been done to foster this highly profitable branch of the country’s industry.

Modern Methods of Cultivation

Hatching the Eggs

The merest outline of the modern methods of cultivation will show how highly they have been developed. To begin with, the eggs are placed on sheets of paper or muslin directly after they are laid. These sheets are hung for a few days in a damp atmosphere, and then placed in cold storage for about six months, the period of cold being advantageous for later hatching, which is done by heat.

Growth of the Worms

After hatching, the worm sheds its skin four times. The periods between the “molts,” or ages, vary with different silk worms, but the total process takes about a month. Worms of different ages are always kept separate, being held on large cloth trays which are carried in tiers along the walls of the rearing rooms. The cocooneries where best results are obtained are quiet, spacious, well-ventilated rooms where an even temperature can be maintained. Each worm is kept absolutely clean and has plenty of room, as overcrowding brings disease. As a precaution mild fumigation is resorted to from time to time. Heavy odors or smoke of any sort are not allowed, as these are disturbing to the worms.

Feeding the Worms

The Mulberry Tree

Nourishment is, of course, a very important item for the growing worms, and the best form of food for theBombyx moriis the leaf of the white mulberry, which must be young, fresh and dry, but never withered. For this purpose mulberry tree raising has become an important by-industry in itself. Three varieties are found, classified according to the time of budding—early, medium and late. The leaves, therefore, can be found in the correct condition for the various stages in the growth of the worm. The late budding trees are cultivated in more abundance, as the worms are larger at that time and consume more leaves. The soil in which the trees grow is important, as it has been found that one which is rich in certain minerals provides leaves that keep the worms in better physical condition. A cold winter followed by a warm spring develops the leaves well, and the condition of the leaves is one of the most important factors in the whole process.

Early Development

Careful selection of the eggs is another matter of prime importance. When the leaves are almost ready, the eggs are brought out of cold storage and subjected to heat for about a month before they hatch out. When the worm hatches it is about the diameter of a hair and less than three-fourths of an inch long. It gnaws a hole through the end of the egg from which it issues. Nourishment at first is taken by sucking the sap of the leaves, which are at this stage chopped into fine pieces; later the leaves are consumed without the necessity of their being chopped up.

Spinning the Cocoon

The development is very rapid, the worms consuming their own weight daily. During this period, as has been stated, they shed their skins four times, and after the fourth molt—about one month after hatching—they have assumed their full size. From then on hunger lessens, restlessness grows, and the lifting of the fore part of the body indicates the desire to climb and spin cocoons. For this purpose brush and twigs are provided in the trays, to which the worms attach themselves and begin the spinning process. The silk thread is expelled in a semi-liquid form from two openings underneath the mouth, hardening as it comes in contact with the air. The first threads issued are coarse and rough, having the necessary strength to serve as supports and guysfor the cocoon. Gradually the worm is enclosed in the cocoon after three days of continuous spinning, during one of which it is visible and then slowly disappears, though it can be heard working inside.

Worms Feeding

The worm wastes away as its silk glands are exhausted, and becomes a chrysalis, from which the moth escapes after fifteen to twenty days.

A Nest of Cocoons

Cocoons for Breeding

Cocoons to be used for silk manufacture must be submitted to heat soon after they are completed, in order to kill the chrysalis and prevent it from forcing its way out, thus breaking the fibres. A certain proportion of the cocoons of each crop, however, is allowed to go through the natural process, for reproductive purposes. There is an active market in these breeding cocoons, particularly in Japan and China, and a large quantity are exported annually to Europe and the Near East.

Construction of the Silk Thread

The female cocoon is oval and the male cocoon is peanut shaped. The silk itself consists of two parts: fibroin (the silk fibre) and sericin (the gum). The thread is made up of two strands of fibre held together by the gum, and the length of thread in a single cocoon varies from three hundred to fourteen hundred yards. The cocoons are white, yellowish, or greenish, but after the boiling process the color of theBombyx morisilk is pure white.

Japanese Cocoon Market

Tussah and Wild Silk

The preceding description is concerned more particularly with the latter type, from which the largest proportion of the world’s silk supply is derived, but in a general way it applies to the other types also. The most important of these are the Tussah silk of India and China and the Japanese wild silk. The products are coarser and harsher than those of theBombyx mori, and the natural color is brown.

A Japanese Filature

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