Page:Popular Science Monthly Volume 29.djvu/790

770 and thus exposing the young grub to attack as soon as it is born. Pasteur's own researches soon induced him to adopt the same view. The pebrine microbe was long regarded as a true bacterium, successively described as Bacterium bombycis, Nosema bombycis (Fig. 5), and Panistophyton ovale. Balbiani's recent researches tend to show that it should be assigned to another group, much nearer to animals, and designated Sporozoaria. These protista, still regarded as plants by many naturalists, chiefly differ from bacteria by their mode of growth and reproduction, in which they resemble the parasitic protozoaria, termed Psorospermia, Coccidies, and Gregarinidæ.

In Sporozoaria, growth by fission, the rule in all bacteria, has not been observed; this distinction is fundamental. Sporozoaria multiply by free spore-formation in a mass of sarcode substance (protoplasm), resulting from the encysting of the primitive corpuscles (mother-cells). The formation of numerous spores may be observed within the mother-cells, having the appearance of pseudonavicellæ or spores of gregarinidæ and psorospermia (parasites of vertebrate animals). Balbiani forms these organisms, which are found in many insects, into a small group, which he terms Microsporidia.

The ripe spores are the vibratile corpuscles of Cornalia. They closely resemble the spores of some bacilli (B. amylobacter, for instance), and their germination is likewise effected by perforation of the spore at one end, and issue of the protoplasm from the interior. This, however, does not issue in a rod-like form (Bacillus), but in that of a small protoplasmic mass, with amœboid movements, a characteristic not observed in any bacterium (Balbiani). The other species of silk-worms which have been recently introduced, notably the oak silk-worm from China (Attacus Pernyi), are attacked by microsporidia analogous to those of pebrine.

Pasteur has indicated the mode of averting the ravages of this disease. He has thus addressed the breeders: "If you wish to know whether a lot of cocoons will yield good seed, separate a portion of them and subject them to heat, which will accelerate the escape of the moth by four or five days, and examine them under the microscope to ascertain whether corpuscles of pebrine are present. If they are, send all the cocoons to the silk-factory. If they are not diseased, allow them to breed, and the seed will be good and will hatch out successfully. In a word, start with absolutely healthy seed, produced by absolutely pure parents, and rear them under such conditions of cleanliness and isolation as may insure immunity from infection." When the disease is developed, fumigation with sulphurous acid is recommended, or preferably with creosote or carbolic acid, which do not affect the silk-worms (Béchamp), and which hinder the development of microsporidia. These fumigations likewise keep the litter from