Part 19

In the large rearing houses there is a special chamber for the incubation. Various simple, convenient, cheap apparatuses, whose main object is to create a permanent warm and damp atmosphere, whose degree of heat can be regulated at will, have been proposed. M. Louis Leclerc, in his pamphlet entitled "Petite Magnanerie," has given a description and drawing of a little box which is very useful for facilitating the hatching of eggs. We refer those of our readers who wish for further information on the subject to that work. As soon as the worms are hatched, the eggs are covered with net, and over this are placed mulberry boughs, covered with tender leaves, on which all the little worms congregate. They are then lifted up with a hook made of thin wire, and the worms are placed on a table covered with paper, leaving a proper space between each. They are given, as their first meal, tender leaves cut into little pieces with a knife. These are the operations gone through for the two raisings of worms on the second and third day of the hatching. During this first age they give them from six to eight meals a day, taking care to distribute their food to them as equally as possible. The first meal is given at five o'clock in the morning; the last at eleven or twelve o'clock at night.

When the moult is approaching, the young ones are made to climb on to boughs having tender leaves, so that they can be moved to litters as thin and clean as possible, and there sleep in a good state of health. When the mass of worms is well awake again, the next thing to do is to take them off the litter on which they moulted, and to give them food. If this problem were proposed to a person strange to the operation which is now occupying our attention--to separate the worms from the faded and withered food upon which they are reposing, without touching them--he would certainly be very much at a loss what to answer. The solution of this problem presented for a long time great difficulties, and occasioned numerous reverses in the rearing. Now-a-days, thanks to the employment of a net, the _délitement_, or taking them off their bed, has become an easy operation.

Over the worms, placed on a table, is spread a net, the meshes of which are broad enough to allow them to pass through. On this net are spread the leaves which are to compose a meal. The worms immediately leave the old food, and get on to the new leaves. They then lift the litter with the worms, and throw away the old leaves, now unoccupied, clean the table, and replace the net with the worms. At the next _délitement_ the first net is found under the litter. Figs. 211 and 212 represent two forms of these nets made of thread.

Thread nets, which were of great use, have been supplanted lately, with great advantage, by paper ones, which were invented by M. Eugène Robert. These are leaves of paper, of a peculiar manufacture, pierced with holes proportioned to the size of the worms which are to pass through them. The paper net can be used advantageously also for separating the worms that are too near together, or, as they say, for the _dédoublement_. Formerly, the _délitement_ and the _dédoublement_ were done by hand--a tedious work, and one that presented serious disadvantages. Now-a-days, as we have seen, the worms themselves perform these two perilous operations.

At the second age they still cut the leaves for the worms, but into larger pieces, and proportioned to their size. During the day the temperature of the room ought to be kept to 21° Centigrade, but it may be lowered by 1° or 2° during the night. Towards the end of this age they have only four meals. When the worms are on the point of going to sleep, their meals are decreased.

During the third age the number of the meals is kept to four, the first being given towards five o'clock in the morning, and the last between ten and eleven o'clock at night. The leaf is cut into much larger pieces, and distributed as equally as possible. The _délitement_ and the _dédoublement_ are proceeded with as in the preceding age. One begins to find pretty often during this period of the life of worms, some _luisettes_--that is to say, worms which have not strength enough to moult. They are larger than those just woke up, and that have not as yet eaten, and are shiny. They must be carefully removed, for they will not be long before they die, and infect the air of the room.

During the fourth age they no longer cut the leaves, but give them a great deal more at once. The result is that the litters increase in thickness, and that the _délitement_ must be performed oftener; for the rest, four meals are always necessary. Many _luisettes_ may be seen during the fourth age. The moult which follows the fourth age is the most critical phase in the life of the silkworm. During their sleep they are a prey to acute suffering, and are plunged into a state of lethargy which resembles death. The dryest and cleanest litters diffuse very soon a sickly smell. This moult lasts from thirty-six to forty-eight hours. During this time the room should be kept to at least 22° Centigrade.

When they awake out of this last sleep the attendant should continually be on his guard, as it is then that diseases break out. The worms suffering from these different diseases have received different names. There are besides the _luisettes_ the _arpians_--that is to say, worms that have exhausted all their energy in the work of the last moult, and have not even strength to eat--the _yellow_, or _fat_ worms, which are swollen, of a yellowish colour, and which very easily die; the _flats_ or _mous_, the soft or indolent ones which, after having eaten a great deal and become very fat, die miserably, and enter into a state of putrefaction. And lastly, it is at this age that the _muscardine_, which hardly shows itself at any other age of the insect, appears with great intensity.

The _muscardine_ is a terrible scourge to the rearers of silkworms. The losses which result from this disease in France are estimated at at least one-sixth of the profits. No particular symptom allows of our recognising the existence of this disease in worms which, however, contain its germ; only, the worm, which has eaten up to that time as usual, appears almost in a moment to change to a duller white; its movements become slower, it becomes soft, and is not long before it dies. Seven or eight days after its death it becomes reddish and completely rigid. Twenty four hours afterwards a white efflorescence shows itself round the head and rings, and soon after the whole body becomes floury. This flour is a fungus called _Botrytis bassiana_, of which the _mycelium_ develops itself in the fatty tissue of the caterpillar, attacks the intestines, and fructifies on the exterior. This fungus has been considered as the immediate cause of the _muscardine_, and has been also regarded as the last symptom or end of the disease. The communication of the disease by contagion has alternately been admitted and denied. As its true cause, and any efficacious means of opposing it, are still unknown, the breeders of silkworms must be content to apply--so as to prevent or struggle against this dreadful scourge--the precepts of hygiene: good ventilation, excessive cleanliness, frequent _délitements_, and good food properly prepared.

After the _muscardine_, we must mention another epidemic disease still more terrible, the _gattine_. This disease shows itself from the very beginning of the rearing, and increases in intensity at each age, so that the number of worms able to enter regularly into the moult becomes smaller and smaller. We are still in a state of utter ignorance as to the cause of this last affection, which has occasioned, for the last ten years, incalculable losses in the rearing houses, which threatens the silkworm with complete destruction, and which in the meanwhile has ruined the unfortunate countries of the Cévennes, the principal seat of sericulture in France.

During the fifth age, the worms become large so quickly that on the fifth or sixth day they are obliged to be moved away from each other on the litter. The _délitement_ must be made every two days, or indeed, every day now, on account of the enormous amount of the excrement; and, at the same time, a good ventilation must be constantly maintained. The temperature of the room should now be kept to 24°, without ever exceeding this degree of heat. When it is perceived that the worms wish to ascend, or _mount_, there are placed on the tables, at certain distances from each other, little sprigs of heather or very dry branches of light wood.

When the worms begin to mount into the heather, one must _encabaner_--that is to say, form with these branches little hedges, curved back like a hut or cradle, the openings of which are, on an average, seventeen inches or so (Fig. 213). At the expiration of twenty-four hours all the good worms have mounted. The laggards who remain under the _cabanes_ are taken off by hand, and placed on a table, which is immediately _encabanea_.

The cocoons spun on these branches of heather ought to be large, heavy, and well-shaped. The good cocoons are regular; their ends are rounded and not pierced; and they are hard, especially at their extremities, and have a fine grain. They are cylindrical. The best are drawn in towards the middle, or have a concavity on either side of it (Fig. 215). Every one knows that there are white and yellow cocoons. They are the produce of different races of worms.

Commerce recognises two kinds of white silk: the _first white_ and the _second white_. The silk of the _first white_ is produced by the race _Sina_, the cocoons of which are of a perfect and azured white. They produce the most beautiful and most precious silk, and serve for the fabrication of light and delicate coloured tissues. The silk of the _second white_ is furnished by two races: the _Espagnolet_ and the _Roquemaure_.

The races that produce yellow cocoons are more numerous than the white ones. The yellow races are divided into three groups: those that have small, middle-sized, or large cocoons. The first and second are stronger, and more esteemed than the last.

The greater number of the races of silkworms have, let us here mention, white and yellow cocoons; there are some, however, whose cocoons are of a greenish white, or even quite green, or of a reddish green. One race, raised in Tuscany, near Pistoia, has cocoons of a pale rose colour; and, lastly, mention has been made of cocoons of a purple colour.

When the cocoons are completed, the people in charge of the rearing establishments separate them from the heather and sell them to the silk-spinners. But they must manage to get these cocoons into a state in which they will remain entire during a long time. They must, in other words, kill the chrysalis, to prevent the cocoons being pierced by the moth. To kill the chrysalis so as to prevent the development of the imago is an operation which is called the _étouffage_, or stifling.

To effect this stifling, the cocoons are exposed to a high temperature. Formerly, in the Cévennes, the cocoons were placed in a baker's oven, heated for baking bread. But they ran the risk thus of being burnt, or of a certain number of chrysalides remaining alive. Now, to kill the chrysalides, they make use of steam at 100°, produced by water boiling in a vessel, and which passes through wicker baskets filled with cocoons.

The rearer must also take care at the time he gathers them, to separate the cocoons which are to provide eggs for the next year. As the female cocoons are heavier than the male cocoons, they are easily separated by weighing them in a pair of scales.

To obtain the eggs, or grain, the cocoons are fixed on sheets of brown paper, covered with a slight coating of paste made of flour. They are arranged in such a manner that the moths shall find no obstacle when they come out of them, head foremost; and, moreover, so that they may be able to reach with their legs the cocoon which is opposite them, so as to hang on to it, and to facilitate their exit from their own cocoon (Fig. 218). The male and female cocoons are pasted on separate sheets.

It is from fifteen to twenty days after the _montée_, or _mounting_, and when the temperature of the rooms has been kept between 20° and 25°, that the moths begin to be hatched. As they appear, they are seized by the wings and placed on cloths stretched out for the purpose, where they are left for about an hour, till their wings have fallen flat on their bodies. As soon as they have evacuated a red liquor, the males and females, which up to that time have been apart, are put together.

They then stick sheets of paper on to screens, putting from twenty-five to thirty females on each sheet (Fig. 219). It is here the moths lay their eggs. The sheets of paper, covered with eggs, are then hung on wires, at a small distance from the ceiling of a room having a northern aspect, which is never warmed. They remain thus, exposed to all variations of temperature, till the return of the warm weather. We will say a few words, to bring this subject to an end, on the winding of cocoons and the spinning of silk.

The winding of cocoons is an operation which at first sight appears very simple, but which is in reality a difficult and delicate process. It requires unremitting attention, great experience, and a delicacy of touch which can only be found in the fingers of woman, or rather, in the fingers of certain women.

The woman who is spinning, stands before a sort of loom which is called _tour_ (Fig. 220). Under her hand is a copper containing water, which she heats to the required degree by opening the tap of a tube, which brings a current of steam. She plunges the cocoons into the hot water, and moves them about in it, to soften the gummy substance which sticks the silken threads of the cocoon together. Then she beats them, with a light hand, with a small birch-broom. The threads of the cocoons get caught in the extremities of the twigs of which the little broom is made, and the workwoman seizes with her fingers the bundle of threads, and shakes them about till she perceives that they are all single, and in a fit state to be joined together.

Let us suppose that it is wished now to make up a _brin_, or staple, by uniting together the ends of five cocoons. She chooses five ends in the mass, makes of these a bundle, and introduces it into the hole of a _filière_. She makes two staples (_brins_) at once, one on her right, the other on her left hand. She then brings them together, she crosses them, rolls them, and twists them, the one on the other, several times; after which, she separates them from above and keeps them well apart, making each of them pass into a hook at a distance, from which they are going to twist round into a hank, separately, on a wheel. The two threads thus twisted are drawn close together, compressed, and become one, getting round by rolling on each other, and being kept in continual motion, drawn out as they are by the rapid motion of the wheel.

The difficulty which the emptying the cocoon of its silk thread presents, makes us understand what difficulties those manufacturers must have met with who have lately attempted to extract from the stalks of mulberry leaves a sort of silk. We will enter into no details of the attempts which have been made to accomplish this object in our time, attempts which have, however, been crowned with no success whatever. We will confine ourselves to reminding the reader that these attempts are far from being of recent origination, since they date back to as far as Olivier de Serres, the father of French sericulture.

In a little work published by Olivier de Serres, in 1603, under the title of _Cueillette de la Soie_, "The Gathering of Silk," we find a memoir entitled: _La second richesse du mûrier, qui se trouve en son escorce, pour en faire des toiles de toute sorte, non moins utile que la soie provenant d'icelui_, "The second wealth of the mulberry tree which is found in its bark, how to make of it cloth of all sorts, not less useful than the silk derived from this tree." Olivier de Serres proves in this memoir that the second bark, or _liber_, of the mulberry tree contains a fibre capable of replacing hemp or flax, and he describes the processes by which this may be obtained. The processes which had been proposed by Olivier de Serres in 1603, were resumed in the Cévennes a dozen years ago by M. Duponchel on the one hand, and on the other by M. Cabanis,[64] who operated on the bark instead of taking the whole of the wood of the mulberry tree. But none of these attempts have given any good results up to the present moment.

[64] See the "Année scientifique," 7e année, p. 432.

The various diseases which for the last fifteen years have been so fatal to the mulberry silkworm, have suggested the idea of acclimatising in Europe other silk-producing Bombyces, if not with the view of superseding, at least as auxiliaries to the mulberry species. The genus _Attacus_ has furnished these auxiliaries. Among the species which have, in this respect, the greatest claims to our attention, we must place in the first rank those which feed upon the leaves of the oak tree. Indeed, the trees which can be made use of for their cultivation are very numerous in Europe, and, moreover, the silk produced by these worms appears to possess superior qualities.

There are three oak-feeding species of the genus _Attacus_. They are _Yama-Maï_, _Pernyi_, and _Mylitta_.

The silk of _Yama-Maï_ is as bright as that of the mulberry silkworm, but a little less fine and strong, and occupies the first rank after it. If we could succeed in acclimatising this species it would supply any deficiency there might be in our crops of ordinary silk.

The eggs of the _Attacus Yama-Maï_ were brought from Japan--where this worm is reared--conjointly with the mulberry silkworm, in 1862. The larvæ hatched at Paris, in 1863, were green, of a great size, remained in that state eighty-two days, and were easily reared. Their cocoon resembles that of the mulberry species. It is composed of a beautiful silk of a silvery whiteness in the interior, and of a more or less bright green on the exterior. The moth is very large and beautiful, of a bright yellow colour, approaching orange.

We give a drawing of the _Attacus Yama-Maï_, taken from the plates which accompany M. Guérin-Méneville's memoir.[65]

[65] Sur le Ver à Soie du Chêne, et son Introduction en Europe. Extrait du Magasin de Zoologie, 1855, No. VI.

[For an account of experiments conducted in England by Dr. Wallace, whichunfortunately were complete failures as far as rearing the moth went, see an essay by that gentleman in _The Transactions of the Entomological Society of London_, 3rd series, vol. v., pt. 5; Longmans and Co. The results of an experiment which give the greatest hopes of success, will be found in "The Entomologist" for October, 1867.--ED.]

Fig. 221 represents the larva, or caterpillar, two-thirds natural size; Fig. 222, the cocoon, drawn on the same scale; and Fig. 223, the moth.

In 1866, M. Camille Personnat published a very interesting monograph of _Yama-Maï_, which may be consulted with profit by both cultivators of silk and naturalists.[66]

[66] Le Ver à Soie du Chêne (_Bombyx Yama Maï_), son histoire, sa description, ses moeurs. 8vo., avec planches coloriées. A Laval, à l'école de sériculture.

_Attacus pernyi_ yields a remarkably beautiful silk, fine, strong, and brilliant, which can be spun and dyed with great ease. The tissues obtained from it partake of the qualities of ordinary silk, of wool, and of cotton. This species of _Attacus_, which is reared on the oak in Mandchouria, has given rise to great hopes in France. The cocoons and moths of this worm were exhibited for the first time at the Universal Exhibition of 1855. They were reared by M. Jordan, of Lyons, from some cocoons sent over from China by the missionaries. It is much to be desired that this species may be acclimatised in Europe.

Figs. 224 and 225 represent, after drawings in the Memoir of M. Guérin-Méneville, already referred to, the cocoon and moth of the _Attacus pernyi_.

The silk which _Attacus Mylitta_ produces is perhaps superior to that of _Pernyi_. When the cocoons are properly prepared, the silk can with ease be wound off from one end of them to the other. This worm is found in various parts of Bengal and of Calcutta, and also at Lahore, and its silk is exported in considerable quantities under the name of _tusseh_. Brownish stuffs are made of it in India of firm and bright texture, which are used for summer clothing, or for covering furniture.

Figs. 226 and 227 represent the moth and the cocoon of _Attacus Mylitta_ after M. Guérin-Méneville.

In 1855 M. de Chavannes reared this species in the open air, near Lausanne, in Switzerland. This treatment succeeded perfectly, without any degeneration, for many years. It, however, died out at last, from the effects, perhaps, of too great a difference in the climate, or from those accidents, still so little understood, to which even the insects of our own country are subject. This was unfortunate, as this species is one of those whose acclimatisation in Europe is the most to be desired, for it would render great service to the cultivators of silk.

It remains for us to speak of two other species, which are very important, inasmuch as their domestication in Europe is now an accomplished fact. We mean the _Attacus_ or _Bombyx_ of the Ailanthus, and also that of the Castor-oil plant.

Every one has heard of the Ailanthus silkworm (_Attacus_ [_Bombyx_] _Cynthia_), whose acclimatisation in Europe has been materially assisted by the admirable and persevering efforts of M. Guérin-Méneville.

The Ailanthus worm is a native of Japan and of the north of China. It was brought over in 1858 by Annibale Fantoni, and sent to M. Guérin-Méneville by MM. Griseri and Colomba, of Turin. When it is nearly full-grown it is emerald green, with the head, the feet, and the last segment of a beautiful golden yellow, and has black spots on each segment. This worm, in its full-grown state, is represented by Fig. 228; in the same figure are also represented the eggs and the cocoon. The moth has the abdomen yellowish underneath, with little white tufts. Its wings are traversed by a white band, which is followed exteriorly by a line of a bright rose; each wing is also marked by a lunula or crescent-shaped spot.