THE CORPUSCULAR DISEASE [pEBRINE] 149 



We shall see that Pasteur has nothing to lose from this 

 attentive study of the progress of his mind. He some- 

 times wandered in his research, as we have said, allowing 

 himself to be deceived by false gleams, but he always re- 

 turned to the right path, and it is just this struggle with 

 error, always imminent, that makes the interest of this 

 study. 



II 

 THE CORPUSCULAR DISEASE [PfiBRINE] 



Some preliminary notions and details are necessary 

 to understand thoroughly the moving vicissitudes of 

 this struggle against a scourge as redoubtable as was 

 the disease of silkworms at this time. Everybody knows, 

 at least in a general way, the principal phenomena of the 

 life of the silkworm: its birth from an egg, whose re- 

 semblance to certain vegetable seeds has led to its being 

 given the name of graine; and its four molts or changes 

 of skin, during which the worm ceases to eat, remains 

 motionless, seems to sleep upon its litter [feeding place], 

 and clothes itself, under its old skin, with a new supple 

 and elastic skin, which allows to it a new development. 

 The fourth of these molts is followed after two or three 

 days by a period of extreme voracity during which the 

 worm increases in volume rapidly and acquires its maxi- 

 mum size: it is the big gorge. This period terminated, 

 the worm eats no more, moves about uneasily, and if 

 sprigs of heather on which it can ascend are offered, it 

 hastens to choose thereon a suitable place to spin its 

 cocoon, a kind of silky prison which permits it to undergo 

 in peace its transformation first into a chrysalis, and 

 then into a moth. In this cocoon, the body of the worm, 

 emptied of all the silky matter, contracts and covers 



