30 



KNOWLEDGE 



[Fbbruaby, 1902. 



import-ed raw material when worked up into silk goods 

 would probably not be more than between two and 

 three millions; and it would thus appear that out of 

 a total consumption of some twenty-two or twenty-three 

 millions sterling worth of manufactured silk only a very 

 small fraction is made at home. 



The British silk industiy has, indeed, been gradually 

 languishing and diminishing for a period of something 

 over sixty yeaJ^s — practically during the whole of the 

 Victorian era. In 1838, according to the same source 

 of information, when the population of the British Isles 

 was onl)' twenty-five millions, the annual consumption 

 of home-made hand-loom woven silken goods was 

 equivalent to eight shillings and sixpence per head. 

 In 1898, on the other hand, when the population was 

 reckoned at about thirty-eight millions, the consumption 

 of silk goods manufactured abroad was equivalent to 

 ten shillings and sixpence per head, while that of British- 

 made silk reached only a miserable eighteenpence per 

 head. 



It is not that hand-woven British goods are inferior 

 in quality and wearing power to the foreign articles 

 by which they have been so largely supplanted. Quite 

 the contrary. And now that raw silk is exported from 

 India, China, and Japan in much better condition for 

 manufacture and at a lower price than in 1838, there 

 seems no reason why it should not pay to work it up in 

 this countiy. 



Although the caterpillai-s of many species of moths 

 niake silken cocoons for the protection of their chrysar 

 lids, and the cocoons of several of these are used to sup- 

 ply commercial silk, the great bulk of the supply is 

 r Horded by the caterpillar of the silk-moth, the so-called 

 " silk-wonn." Curiously enough, the silk-moth is a 

 purely domesticated animal, whose wild ancestor is now 

 unknown. Even the real home of this insect is not 

 definitely ascertained, some authorities believing 

 northern China to be the original habitat of Biiiiilnjr 

 won', as the species is technically called, while others 

 think that Bengal has a stronger claim to the honour. 

 Be this as it may, the species has been domesticated 

 for an immense period in China, some say since about 

 1640 B.C.; it was introduced into Constantinople in 

 the sixth century of our era. whence it was can-ied into 

 France in the year 1494. It is now distributed over 

 a large portion of the globe ; and as a consequence of 

 such a wide range and such a long period of domesti- 

 cation it has altered considerably from the parent form, 

 and has likewise developed several local modifications. 

 Evidence of its alteration from the parent form (what- 

 ever that may be) is afforded by the aborted condition 

 of the wings of the adult moth, which arc so weak as 

 to render the insect incapable of flight. By some it 

 has been said that if the moths be reai-ed in the open 

 air in perfect freedom they will recover the power of 

 flight in the course of a few generations, but since it is 

 also stated that the caterpillars when turned out on trees 

 are helpless, this requires confirmation. Variation is 

 shown by the fact that in one breed the cocoon is yellow 

 while in another it is white; and this, coupled with 

 other variations, has led some authorities to believe 

 that the domesticated form is derived from more than 

 one wild species. This view has, however, not met with 

 general accept-ation. 



The silk is found within the body of the caterpillar 

 in a pair of glands of somewhat complex structure, and 

 is there in a viscid condition. The ducts of the two 

 glands unite into one common channel, so that their 

 products are united before emission into a single thread. 



which in the last part of the apparatus is coated with 

 a kind of waterproof varnish. As " silkworms," pro- 

 bably owing to the artificial conditions under which 

 they arc reared and in-and-in breeding, are subject 

 to many diseases, especially about the period of pupa- 

 tion, attempts have been made to convert the viscous 

 matter in the bodies of the caterpillars into silk by 

 artificial means. But although the secretion can be 

 drawn out into threads of considerable fineness, it 

 resembles catgut rather than silk, and has no power 

 of resisting the effects of water. A still more bold 

 attempt has been made, namely, to obtain silk direct 

 from the mulberry leaves on which the silkworm feeds ; 

 but this, as might have been expected, resulted in com- 

 plete failui-e, many of the workings in nature's organic 

 laboratories being too subtle for imitation by any of 

 the means at man's disposal. It may be added that 

 although silk of good quality is produced by silkworms 

 reared in Britain, the thread is so short as to render 

 it of little or no commercial value. 



The best and most valuable silk is yielded by the 

 white cocoons ; but of these there are two descriptions, 

 known in the trade as first and second w^hite. The 

 yellow cocoons, which ai-e the most numerous, are 

 divided into three classes according to size; the small 

 and medium-sized cocoons being of higher value than 

 the larger ones. The cocoons of other breeds vary in 

 colour from greenish white to pure or reddish gi'een ; 

 while there exists a Tuscan breed of silkworm which 

 produces pale rose-coloured cocoons, and purple cocoons 

 have also been reported. The breed yielding white 

 cocoons, known in France as sina, appears to have 

 been produced from the yellow-cocoon breed by careful 

 selection, since a certain percentage of yellow cocoons 

 always appears among the white ones. By the exercise 

 of great care the percentage of yellow cocoons, which 

 fonnerly had been much largei', was reduced many 

 years ago in France to a very few per thousand. 



The silk-moth is the typical representative of a 

 family of moths (Bomhycidce), characterised by the 

 absence of a proboscis, and the presence of one internal 

 nei-vui'e on the hind-wing. A second family of silk- 

 producing moths — the SaturniidcE — diflFer from the 

 Bomhycidce by the presence of two or three nei-vures 

 in the hind-wing. Among these are some of the largest 

 of all moths ; and the majority of them are characterised 

 by the presence of a clear transparent spot or " window '' 

 in the centre of each wing ; the transparency being, 

 of course, due to the absence on these areas of tha 

 minute scales which cover the remainder of the wings. 

 Hence they may convenientl)' be called window-moths. 

 The use of this veiy peculiar type of marking is at 

 present quite unknown, but it is probably of some con- 

 siderable importance in the economy of these insects. 



In Japan the great silk producer is a lai'ge yellow 

 window-moth, measuring nearly seven inches across the 

 wings, known as the yama-mai {Attacus yamamai). the 

 caterpillar of which feeds on oak-leaves. It produces 

 large green cocoons yielding an excellent silk, second 

 only in quality to that of the silk-moth. For a long 

 time the exportation of this insect was forbidden, but 

 eggs from time to time found their way to Europe, where 

 attempts were made to acclimatize such a valuable 

 species. All these attempts were, however, attended by 

 failure. Although the cocoons are bright gi'een, the 

 silk in their interior is of a silvery white. 



Another species which it has been attempted to intro- 

 duce into France is the Manchm-ian window-moth 

 {Attacus perryi), whose caterpillar likewise feeds upon 



