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.
| Fig. 211.—Lozenge-shaped net. | Fig. 212.—Square net. |
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.