172 Pasteur: the history of a mind 



silk-growers, "whether a lot of cocoons will give you sound 

 eggs? Take a portion of them and heat them so as to 

 hasten four or five days the hatching of the moths, and 

 see whether the latter are corpuscular. The micro- 

 scopical examination of the moths is easier and more 

 certain than that of the eggs because in them the cor- 

 puscles are many times more abundant. If the moths 

 are bad, send the cocoons to the spinning mills. On 

 the contrary, if you find that only a very limited number 

 of individuals are diseased, allow them to develop: 

 the eggs will be good and the brood which you mil have 

 from them the next year will be a successful one. Only, 

 this brood will be unfit for breeding because of the initial 

 presence and multiplication in it of the corpuscles. 

 But do you wish the brood to be sound up to the very end 

 and give you perfect eggs? Then take absolutely sound 

 eggs, coming from absolutely pure parents, and hatch 

 them in conditions of cleanliness and isolation, such 

 that infection cannot spread there. But if, unfortu- 

 nately, the disease should appear I still give you the 

 means of making a selection, and of separating rigorously 

 the sound eggs from the corpuscular ones." 



The problem was, therefore, solved, and the victory 

 could be considered complete. Let us hasten to say that 

 no part of it is more widely discussed at the present time. 

 The examination of eggs with the aid of the microscope 

 which had been judged impossible has become a custom. 

 The growers of silkworms have made it encircle the globe 

 as they once did the disease itself, and pcbrine has 

 ceased to haunt the mind of those engaged in the silk- 

 worm industry. On one point only were the expecta- 

 tions of Pasteur unfulfilled. He hoped that it would be 

 possible to make the disease disappear. This was a 

 noble ambition and would have been a great example. 

 Experience has shown that it was impossible. This is 



