4 PLAGUE AMONG SILK WORMS. 



Pasteur found by experiment that certain changes which some- 

 times take place in beers and wines, during the course of pre- 

 paration for use, and which he calls " diseases," are owing to the 

 presence of vegetable germs, every particular change being due 

 to a different kind of germ. Another investigation, which he 

 undertook at the earnest entreaties of his friend and preceptor 

 Dumas, the celebrated chemist, resulted in a discovery which 

 throws interesting light on the same subject, by showing how 

 animal germs may be the cause of a disease among animals of a 

 very destructive and infectious kind. France, a few years ago, 

 was threatened with a great calamity. For fifteen years a plague 

 had raged among its silkworms. In 1852 the silk culture of 

 France yielded a revenue of 160,000,000 of francs; ten years 

 later it had fallen to 4,000,000. Pasteur found that the bodies of 

 the silkworms which had the disease were infected by minute cor 

 puscles, which, taking possession of the intestinal canal, spread 

 thence throughout the body. They filled the silk cavities, the 

 Btricken insect often going through the motions of spinning with- 

 out any material to answer to the act. The organs, instead of 

 being filled with the viscous liquid of the silk, were packed to dis- 

 tention by these corpuscles. On this feature of the plague Pasteur 

 fixed his whole attention, and brought the inquiry to a triumphant 

 issue! By inoculating the healthy worms with the corpusculous 

 matter, he found the disease to be highly infectious. He further 

 showed how the silkworms infected one another by inflicting 

 wounds upon each other by means of their claws. He washed 

 the claws, and found the infecting corpuscles in the water. He 

 next spread the infection by simply bringing the healthy and 

 diseased into contact. The diseased worms sullied the leaves of 

 the mulberry tree among which they spin, and by their dejections 

 spread infection in both ways.* 



These observations exemplify in the most striking manner 

 what actually takes place in some of our own zymotic diseases. 



Whatever be the difference of opinion as to the precise nature 

 * (Tyndall "Dust and Disease.") 



