76 Mr. A. B. Farn on the Silkworm Disease. 



parasite ; and 30 one might reasonably anticipate some small 

 number at least of healthy worms would hatch from any given 

 seed. The infected ova would produce infected worms doomed 

 to an early death, yet not dying before they would become 

 a source of infection to healthy worms feeding with them. 

 Pasteur observed that a very large number of worms which had 

 not inherited the disease but had become infected somewhat late 

 in life, attained almost their full growth, and would mount into 

 the twigs provided for them in which to spin their cocoons, and 

 then, although moving their heads from side to side, and going 

 through all the motions of spinning cocoons, they produced no 

 silk whatever. They seemed spinning invisible cocoons with 

 invisible silk. 



Upon making a post-mortem examination of such worms it 

 was found that the glands, which in a normal condition would 

 have produced that wonderfal fluid which as it is ejected by the 

 worm dries and forms silk, were crammed by the Pebrine para- 

 site, to the total exclusion of the silk secretion. On this circum- 

 stance, and the fact that the silk-glands at all times seem most 

 infected, Pasteur founds his hypothesis that the silk-glands are 

 the proper habitat of these parasites. He says as the habitat of 

 the tapeworm is the large intestine, as muscle is the locality for 

 trichina spiralis, so the glands of the silkworm are the chosen 

 home of the Pebrine parasite. 



As regards the propagation of the parasite itself, it would seem 

 to be in this fashion. At a certain period of its existence it loses 

 its glistening appearance. As it becomes duller small granular 

 particles are formed in its interior ; these increase in size until 

 at last the capsule of the parent parasite separates, and allows 

 the nuclei to escape, and these then commence an independent 

 existence, gradually developing into the glistening full-sized 

 parasite. 



The discovery that Pebrine may become an hereditary disease 

 not only explained the extermination which overtook some entire 

 broods, but at the same time furnished the clue to a practical 

 means of predicting the probable result of rearing the worms of 

 any batch of seed. If, upon crushing a few ova and examining 

 their fluid contents under a microscope, a very large number of 

 parasites are discovered, it may safely be predicted that the 

 rearing of the worms from this seed will be disastrous. And 

 upon a more or less abundance of the parasite under such micro- 

 scopical examination of the seed will depend the prediction as to 

 the more or less success in rearing worms from such and such a 

 stock. I may say that I had three samples of seed submitted to 

 me for microscopical examination and opinion. Belying entirely 

 upon Pasteur's guidance in the matter, I predicted " total failure," 

 «' almost total failure," and " fairly good results" respectively as 



