THE DISEASES OF SILK WORMS 129 



but the disease would attack the chrysalis, which 

 might die in the cocoon or pass through its usual 

 metamorphosis and emerge as a diseased moth. 

 Silk worm moths mate soon after they emerge, and 

 then the female lays her eggs. It was found that 

 eggs from diseased moths produced diseased worms, 

 so that the malady was spoken of as hereditary. 

 It is, in fact, one of the very few diseases which 

 may be transmitted through the germ cells from 

 parent to offspring. 



The disease had made such tremendous inroads 

 upon the silk industry that France was producing 

 but a small fraction of her previous yield of silk. 

 In 1853, France produced 52,000,000 pounds of 

 cocoons; but there were only 8,000,000 pounds, or 

 less than one-sixth as much, produced in 1865. 

 The distress in the silk-producing district was acute. 

 "The traveler," wrote Pasteur, "who fifteen years 

 ago had gone through the mountains of Cevennes, 

 and who retraced his course to-day, would be sur- 

 prised and shocked to see the changes of all kinds 

 which have occurred in so short a time in that coun- 

 try. Formerly he would see, on the slopes of the 

 hills, active and robust men breaking up rock in 

 order to construct solid walls for the support of the 

 fertile but laboriously prepared soil and raising ter- 



