APHORISMS AND REFLECTIONS 



which float in the blood of the fly. These multiply 

 and lengthen into filaments, at the expense of 

 the fly's substance ; and when they have at last 

 killed the patient, they grow out of its body and 

 give off spores. Healthy flies shut up with 

 diseased ones catch this mortal disease, and perish 

 like the others. A most competent observer, M. 

 Cohn, who studied the development of the Empusa 

 very carefully, was 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. 

 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 



