Page:Popular Science Monthly Volume 29.djvu/791

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becoming corrupt, and in a properly conducted nursery the litter is kept dry.

Wrongly confounded with pebrine, the disease flacherie is still more destructive to silk-worms. The symptoms are remarkable. The rearing of silk-worms often goes on regularly up to the fourth molt, and success seems assured, when the silk-worms suddenly cease to feed, avoid the leaves, become torpid, and perish, while still retaining an appearance of vitality, so that it is necessary to touch them in order to ascertain that they are dead. In this state they are termed morts-flats. A few days, sometimes even a few hours, suffice to transform the most flourishing nursery into a charnel-house. Pasteur examined these morts-flats, and found that the leaves contained in the stomachPSM V29 D791 Micrococcus bombycis flacherie microbe.pngFig. 6.Micrococcus bombycis (Cohn) Flacheriemicrobe (x 500 diam.). and intestine were full of bacteria, resembling those which are developed when the leaves are bruised in a glass of water and left to putrefy (Fig. 6). In a healthy specimen, of good digestion, these bacteria are never found. It is therefore evident that the disease is owing to bad digestion, and becomes rapidly fatal in animals which consume an enormous amount of food, and do nothing but eat from morning to night. The digestive ferments of unhealthy silk-worms do not suffice to destroy the bacteria of the leaves, nor to neutralize their injurious effects. These bacteria are really the cause of the disease, for if even a minute quantity of the leaves taken from the intestine of diseased silk-worms be given to healthy specimens, they soon die of the same disease. It is, therefore, essentially contagious, and, in order to prevent the diseased silk-worms from contaminating the healthy by soiling the leaves on which the latter are about to feed, as much space should be assigned to them as possible.

Good seed should also be selected, since it has been ascertained that some lots of seed are more liable to the disease than others. The affection does not indeed begin in the egg, as in pebrine, but the question of heredity comes in. It is clear that, when a silk-worm has been affected by flacherie without dying of it, its eggs will have little vitality, and the grubs which issue from them will be predisposed by their feeble constitution to contract the disease.



THE study of fear, although it is very interesting, has hardly yet been made in a methodical way. While some ingenious observations concerning it may be found in moral and psychological works, the physiologists and philosophers appear to have neglected this