The Life of the Caterpillar 



ment, ought to gain in virulence. So reflec- 

 tion tells us. 



The solvents tried are confined to three: 

 water, spirits of wine and sulphuric ether. I 

 employ the latter by preference, although the 

 other two, spirits of wine especially, have 

 yielded satisfactory results. To simplify the 

 experiment, instead of submitting to the action 

 of the solvent the entire caterpillar, who 

 would complicate the extract with his fats 

 and his nutritive juices, I prefer to employ 

 the cast skin alone. 



I therefore collect, on the one hand, the 

 heap of dry skins which the moult of the 

 second phase has left on the dome of the silken 

 dwelling and, on the other hand, the skins 

 which the caterpillars have rejected in their 

 cocoons before becoming chrysalids; and I 

 leave the two lots to infuse, separately, in sul- 

 phuric ether for twenty-four hours. The in- 

 fusion is colourless. The liquid, carefully 

 filtered, is exposed to spontaneous evapora- 

 tion ; and the skins are rinsed with ether in the 

 filter, several times over. 



There are now two tests to be made: one 

 with the skins and one with the product of 

 maceration. The first is as conclusive as can 

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