BIOLOGY. 261 



which the spore-bearing filaments protrude, is pretty sure to carry 

 off a spore or two. It is ' infectious,' because the spores become 

 scattered about all sorts of matter in the neighborhood of the 

 slain flies. 



" The silkworm has long been known to be subject to 

 a very fatal and contagious and infectious disease called the 

 Muscardine. Audouin transmitted it by inoculation. This dis- 

 ease is entirely due to the development of a fungus, Botrytis 

 Bassiana, in the body of the caterpillar; and its contagiousness 

 and infectiousness are accounted for in the same way as those of 

 the fly-disease. But of late years a still more serious epizootic has 

 appeared among the silkworms ; and I may mention a few facts 

 which will give you some conception of the gravity of the injury 

 which it has inflicted on France alone. The production of silk 

 has been for centuries an important branch of industry in Southern 

 France, and in -the year 1853 it had attained such a magnitude, 

 that the annual produce of the French sericulture was estimated 

 to amount to a tenth of that of the whole world, and represented 

 a money value of 117,000,000 of francs, or nearly 5,000,000 

 sterling. What may be the sum which would represent the 

 money value of all the industries connected with the working up of 

 the raw silk thus produced is more than I can pretend to estimate. 

 Suffice it to say, that the city of Lyons is built upon French silk, 

 as much as Manchester was upon American cotton, before the 

 civil war. Silkworms are liable to many diseases; and, even before 

 1853, a peculiar epizootic, frequently accompanied by the appear- 

 ance of dark spots upon the skin (whence the name of 'Pebrine' 

 which it has received), had been noted for its mortality. But in 

 the years following 1853, this malady broke out with such ex- 

 treme violence, that in 1856 the silk crop was reduced to a third 

 of the amount which it had reached in 1853 ; and, up till within 

 the last year or two, it has never attained half the yield of 1853. 

 This means not only that the great number of people engaged in 

 silk-growing are some 30,000,000 sterling poorer than they 

 might have been ; it means not only that high prices have had to 

 be paid for imported silkworm eggs, and that, after investing his 

 money in them, in paying for mulberry-leaves and for attend- 

 ance, the cultivator has constantly seen his silkworms perish and 

 himself plunged in ruin, but it means that the looms of Lyons 

 have lacked employment, and that, for years, enforced idleness 

 and misery have been the portion of a vast population, which, in 

 former days, was industrious and well-to-do. In 1858, the grav- 

 ity of the situation caused the French Academy of Sciences to 

 appoint commissioners, of whom a distinguished naturalist, M. de 

 Quatrefages, was one, to inquire into the nature of this disease, 

 and, if possible, to devise some means of staying the plague. In 

 reading the report made by M. de Quatrefages in 1858, it is ex- 

 ceedingly interesting to observe that his elaborate study of the 

 Pebrine forced the conviction upon his mind that, in its mode of 

 occurrence and propagation, the disease of the silkworm is, in 

 every respect, comparable to the cholera among mankind. But 

 it differs from the cholera, and, so far, is a more formidable dis- 



