STUDIES OF 1867 169 



giving with certainty eggs that Pasteur was content 

 to call healthy, but which to-day we would say were free 

 from parasites. It was with these eggs, the hereditary 

 conditions of which he knew, that he began the tentative 

 experiments and the large cultures of 1867. 



The first thing which he had to ask himself, since he 

 had not yet renounced the idea of a constitutional 

 disease existing before the appearance of the corpuscles, 

 was whether the districts of silk husbandry truly consti- 

 tuted, as was said over and over, a deleterious center, 

 an infected district, in which the disease and the cor- 

 puscle would appear inevitably, carried by the ambi- 

 ent air into the healthiest broods. This doctrine spoke 

 too much in favor of inaction and indolence, not to have 

 many partisans. 



To this objection Pasteur was able to respond at the 

 end of his preliminary experiments by showing some 

 lots of worms, offspring of non-corpuscular parents that 

 had passed through the entire metamorphosis without 

 being attacked, and had produced eggs which in turn 

 were free from corpuscles, and this too, although they 

 were raised not only in an infected district, but in a 

 silkworm nursery where by the side of them, other lots 

 died from the disease. Not only did the sound worms 

 remain sound, but their general health seemed to be 

 improved, and from 1865 to 1866, from 1866 to 1867, 

 one saw the broods improve just in proportion to the 

 original purity of the eggs. 



Assured now of not seeing the corpuscles appear in these 

 sound lots, one could perform experiments on corpuscular 

 contagion, beginning it at different ages, could repeat 

 on a large scale the experiment of Gernez, and could 

 synthesize the results. This synthesis is most clear, 

 and we may summarize it very simply. 



If we take sound worms and make them swallow or 



