The diseases of silk worms naturally receive much attention. Like those afflicting mankind, they arise from bad air, resulting from too close confinement, bad food, and other adverse causes. The most fatal and wide-spread disease, and one which since 1854 has threatened the extermination of silk worms in Europe, is the _pebrine_. It is due to the presence of minute vegetable corpuscles, which attack both the worms and the eggs. It was this disease which swept off thousands of Mr. Trouvelot's Polyphemus worms, and put a sudden termination to his important experiments, the germs having been implanted in eggs of the Yama-mai moth imported from Japan by M. Guerin-Meneville, and which were probably infected as they passed through Paris. Though the disaster happened several years since, he tells us that it will be useless for him to attempt the raising of silk worms in the town where his establishment is situated, as the germs of the disease are most difficult to eradicate. So direful in France were the ravages of this disease that two of the most advanced naturalists in France, Quatrefages and Pasteur, were commissioned by the French government to investigate the disease. Pasteur found that the infected eggs differed in appearance from the sound ones, and could thus be sorted out by aid of the microscope and destroyed. Thus these investigations, carried on year after year, and seeming to the ignorant to tend to no practical end, resulted in saving to France her silk culture. During the past year (1871) so successful has his method proved that a French scientific journal expresses the hope of the complete reestablishment and prosperity of this great industry. A single person who obtained in 1871 in his nurseries 30,000 ounces of eggs, hopes the next year to obtain 100,000 ounces, from which he expects to realize about one million dollars. [Illustration: The Potato Caterpillar.] CHAPTER V. THE CLOTHES MOTH. For over a fortnight we once enjoyed the company of the caterpillar of a common clothes moth. It is a little pale, delicate worm (Fig. 57, magnified), about the size of a darning needle, and rather less than half an inch in length, with a pale horn-colored head, the ring next the head being of the same color. It has sixteen feet, the first six of them well developed and constantly in use to draw the slender body in and out of its case. Its head is armed with a formidable pair of jaws, with which, like a scythe, it mows its way through thick and thin.