Sericulture

Other

Diseases.—Grasserie is another form of disease in cidental to the silkworm. It often appears before or after the first moult, but it is only after the fourth that it appears in a more developed form. The worm attacked presents the following symptoms: the skin is distended as if swollen, is rather thin and shiny, and the body of the worm seems to have increased, that is, it suffers from fatness, or is engraisse, hence its name. The disease is characterized by the decomposition of the blood; in fact it is really a form of dropsy. The blood loses its transparency and becomes milky, its volume increases so that the skin cannot hold it, and it escapes through the pores. This disease is more accidental than contagious and rarely takes very dangerous pro portions. If the attack comes on a short time before maturity, the worms are able to spin a cocoon of a feeble character, hut worms with this disease never change into chrysalides, but always die in the cocoon before transformation can take place. The causes which produce it are not well known, but it is generally attributable to currents of cold and damp air, to the use of wet leaves in feeding, and to sudden changes of temperature.

Another cause of serious loss to the rearers is occasioned by flacherie, a disease well known from the earliest times. Pasteur showed that the origin of the disease proceeded from microscopic organisms called ferments and vitrios. One has only to ferment a certain quantity of mulberry leaves, chop them up and squeeze them, and so obtain a liquid, to find in it millions of ferments and vitrios. It invariably occurs during the most active period of

feeding, three or four days after the fourth moult up to the rising, and generally appears after a meal of coarse leaves, obtained from mulberries pruned the same year and growing in damp soil. It can also occur from the feeding of damp leaves, e.g., leaves wetted by rain, to the worms or from leaves too freshly plucked and not allowed to wilt slightly. Flacherie is an intestinal disease of the cholera species and therefore contagious. The definite course is not occasioned so much from the ferments which exist in the leaves themselves, but from an arrest of the digestive process which allows the rapid multiplication of the former in the in testines. Good ventilation is indispensable to allow the worm to give out by transpiration the great quantity of water that it ab sorbs with the leaf. If this exhalation is stopped or lessened the digestion in its turn is also stopped, the leaf remains longer than usual in the intestines, the microbes multiply, invading the whole body, and this brings about sudden death. The true remedies con sist in the avoidance of the fermentation of the leaves by careless gathering, transport or packing, in proper hygienic care in ventila tion and in maintaining a proper degree of dryness in the atmos phere in rainy weather, and in the use of quicklime to facilitate the transpiration of the silkworms.