utterly unable to discover in what manner the smallest germs of the Empusa got into the fly.  The spores could not be made to give rise to such germs by cultivation; nor were such germs discoverable in the air, or in the food of the fly.  It looked exceedingly like a case of Abiogenesis, or, at any rate, of Xenogenesis; and it is only quite recently that the real course of events has been made out.  It has been ascertained, that when one of the spores falls upon the body of a fly, it begins to germinate, and sends out a process which bores its way through the fly’s skin; this, having reached the interior cavities of its body, gives off the minute floating corpuscles which are the earliest stage of the Empusa.  The disease is “contagious,” because a healthy fly coming in contact with a diseased one, from 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 neighbourhood of the slain flies.

The silkworm has long been known to be subject to a very fatal and infectious disease called the Muscardine.  Audouin transmitted it by inoculation.  This disease 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 francs, or nearly five millions 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 appearance 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 extreme violence, that, in 1858, 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 thirty millions sterling poorer than they might have been; it means not only