128 LOUIS PASTEUR. 



Their appetites become especially insatiable during 

 the last clays of rearing. All the world is then astir, 

 day and night. Sacks of leaves are incessantly 

 brought in and spread out on the litters. Sometimes 

 the noise of the worms munching these leaves resembles 

 that of rain falling upon thick bushes. With what 

 impatience is the moment waited for when the worms 

 arrive at the last moulting ! Their bodies swollen 

 with silk, they mount upon the brambles prepared 

 for them, there they shut themselves up in their golden 

 prisons and become chrysalides. What days of rejoicing 

 are those in which the cocoons are gathered ; when, 

 to use the words of Olivier de Serres, the silk harvest 

 is garnered in ! 



Just as in all agricultural harvests, this ingather- 

 ing of the silk is exposed to many risks. Nearly 

 always, however, it pays the cultivator for his trouble, 

 and sometimes pays him largely. But in 1849, after 

 an exceptionally good year, and without any atmo- 

 spheric conditions to account for the fact, a number 

 of cultivations entirely broke down. A disease which 

 little by little took the proportions of an epidemic 

 fell upon the silkworm nurseries. Worms hardly 

 hatched, and worms arrived at the last moulting, were 

 equally stricken in large numbers. It mattered little 

 in what phase the silkworm happened to be : in all it 

 was assailable by the evil. 



There is hardly a schoolboy who has not reared in 



