Page:EB1911 - Volume 25.djvu/114

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98
SILK


mentioned by Acosta, but all trace of the culture had died out before the end of the century. In 1609 James I. attempted to reinstate the silkworm on the American continent, but his first effort failed through shipwreck. An effort made in 1619 obtained greater success, and, the materials being present, the Virginian settlers were strongly urged to devote attention to the profitable industry of silk cultivation. Sericulture was enjoined under penalties by statute; it was encouraged by bounties and rewards; and its prosecution was stimulated by learned essays and rhapsodical rhymes, of which this is a sample:—

“Where Wormes and Food doe naturally abound
 A gallant Silken Trade must there be found.
 Virginia excels the World in both—
 Envie nor malice can gaine say this troth!”

In the prospectus of Law’s great Compagnie des Indes Occidentales the cultivation of silk occupies a place among the glowing attractions which allured so many to disaster. Onward till the period of the War of Independence bounties and other rewards for the rearing of worms and silk filature continued to be offered; and just when the war broke out Benjamin Franklin and others were engaged in nursing a filature into healthy life at Philadelphia. With the resumption of peaceful enterprise, the stimulus of bounties was again applied—first by Connecticut in 1783; and such efforts have been continued sporadically down almost to the present day. Bounties were last offered by the state of California in 1865-1866, but the state law was soon repealed, and an attempt to obtain state encouragement again in 1872 was defeated. About 1838 a speculative mania for the cultivation of silk developed itself with remarkable severity in the United States. It was caused principally through the representations of Samuel Whitmarsh as to the capabilities of the South Sea Islands mulberry (Morus multicaulis) for feeding silkworms; and so intense was the excitement that plants and crops of all kinds were displaced to make room for plantations of M. multicaulis. In Pennsylvania as much as $300,000 changed hands for plants in one week, and frequently the young trees were sold two and three times over within a few days at ever-advancing prices. Plants of a single year's growth reached the ridiculous price of $1 each at the height of the fever, which, however, did not last long, for in 1839 the speculation collapsed; the famous M. multicaulis was found to be no golden tree, and the costly plantations were uprooted.

The most singular feature in connexion with the history of silk is the persistent efforts which have been made by monarchs and other potentates to stimulate sericulture within their dominions, efforts which continue to this day in British colonies, India and America. These endeavours to stimulate by artificial means have in scarcely any instance resulted in permanent success. In truth, raw silk can only be profitably brought to the market where there is abundant and very cheap labour—the fact that China, Japan, Bengal, Piedmont and the Levant are the principal producing localities making that plain.

The Silkworm.

The mulberry-feeding moth, Bombyx mori, which is the principal source of silk, belongs to the Bombycidae, a family of Lepidoptera in which are em- braced some of the largest and most handsome moths. B. mori is itself an inconspicuous moth (figs. 1 and 2), of an ashy white colour, with a body in the case of the male not 1/2 in. in length, the female being a little longer and stouter. Its wings are short and weak; the fore pair are falcate, and the hind pair do not reach to the end of the body. The larva (fig- 3) is hairless, of an ashy grey or cream colour, attains to a length of from 3 to 31/2 in., and is slender in comparison with many of its allies. The second thoracic ring is humped, and there


Fig. 1.—Bombyx mori (male).

Fig. 2.—Bombyx mori (female).

is a spine-like horn or protuberance at the tail. The common silkworm produces as a rule only one generation during the year; but there are races in cultivation which are bivoltine, or two- generationed, and some are multivoltine. Its natural food is the leaves of mulberry trees. The silk glands or vessels consist of two long thick-walled sacs running along the sides of the body, which open by a common orifice—the spinneret or seripositor—on the under lip of the larva. Fig. 4 represents the head (a) and feet (a, b) of the common silkworm, while c is a diagrammatic view of the silk glands. As the larva approaches maturity these vessels become gorged with a clear viscous fluid, which, upon being exposed to the air immediately hardens to a solid mass. Advantage is taken of this peculiarity to prepare from fully developed larvae silkworm gut used for casting lines in rod- fishing, and for numerous other purposes where lightness, tenacity, flexibility and strength are essential. The larvae are killed and hardened by steeping some hours in strong acetic acid; the silk glands are then separated from the bodies, and the viscous fluid drawn out to the condition of a fine uniform line, which is stretched between pins at the extremity of a board. The board

Fig. 3—Larva of Bombyx mart.

is then exposed to the sunlight till the lines dry and harden into the condition of gut. The preparation of gut is, however, merely an unimportant collateral manufacture. When the larva is fully mature, and ready to change into the pupa condition, it proceeds to spin its cocoon, in which operation it ejects from both glands simultaneously a continuous and reelable thread of 800

Fig. 4.

to 1200 yds. in length, moving its head round in regular order continuously for three days or thereabouts. The thread so ejected forms the silk of commerce, which as wound in the cocoon consists of filaments seriposited from two separate glands (discovered by an Italian naturalist named Filippi) containing a glutinous or resinous secretion which serves a double purpose, viz. that of helping the thin viscous threads through their final outlets, and the adhesion of the two filaments when brought into contact with the atmosphere.

Under the microscope cocoon silk presents the appearance (fig. 5) of a somewhat flattened combination of two filaments placed side by side, being on an average 1/1200 part of an inch in thickness (see also Fibres, Plate 1.). The cocoons are white or yellow in colour, oviform in shape, with often a constriction in the middle (fig. 6). According to race, &c, they vary considerably in size and weight, but on an average they measure from an inch to an inch and a half in length, and from half an inch to an inch in diameter. They form