LOUIS PASTEUR. 241 



stages of development, but in the final form, the imago or 

 moth stage, it could always, if present, be easily enough 

 demonstrated. By a series of feeding experiments the 

 passage of these vibratory corpuscles was traced along with 

 food into the intestine of the worm, then into the surround- 

 ing tissues ; healthy worms were found to become diseased 

 when they were invaded by these corpuscles. Should a 

 chrysalis stage be reached, instead of a cocoon a mere mass 

 of corpuscles might sometimes be found, whilst those that 

 reached the moth stage were often crammed with corpuscles 

 to such an extent that they never produced eggs at all ; on 

 the other hand, some were still capable of producing eggs, 

 but these eggs in turn, infected from the commencement, 

 could only give rise to diseased worms. Year after year 

 Pasteur, assisted by a band of ardent workers, returned to 

 the attack during the hatching season. His wife and daughter 

 for the nonce became silk-worm farmers ; forcing houses for 

 artificial hatching were erected, and at last the "peppered" 

 condition of the silk-worms (they are mottled by dark 

 patches scattered over the body, hence the name pebrine) 

 was traced to its true cause. It was demonstrated also that 

 these corpuscles could find their way into worms through 

 the wounds made in each other by means of the sharp hooks 

 which are placed at the ends of their six fore feet, which, 

 passing over the excreta-infected leaves, and then over the 

 skins of their fellows, transfer the corpuscles that have been 

 voided from the alimentary canal of an infected worm to 

 wounds made in a healthy worm. Although drying renders 

 these corpuscles innocuous, this must, under ordinary 

 circumstances, be continued for several weeks, and the dry 

 dust in the earlier stages of the process still remains capable, 

 if blown about and carried to the mulberry leaves of un- 

 affected farms, of spreading the disease to healthy stock. 



What was to be clone ? The remedy was simple. As 

 soon as the moths have paired they are set apart, each pair 

 on a little piece of linen. As soon as the female has laid 

 her eggs, she is pinned by the wings to the corner of the 

 cloth where she is allowed to dry. When the leisure time 

 of the silk-worm cultivator arrives in autumn and winter, 



