168 PASTEUR: THE HISTORY OF A MIND 



to this doctrine, was somewhat astonished that Pasteur 

 saw in his experiment only the practical side and did 

 not flash everywhere the light which shone out of it. 

 In reality, Pasteur had not seen it. The proof is that 

 this experiment was announced to the Academy by him 

 the 26th day of November, 1866, and that in January, 

 1867, he was still asking himself whether the disease 

 was parasitic, and was still advancing against this idea 

 the arguments which we have just examined. He 

 changed his opinion on this subject only during the 

 course of the year 1867, and this change of front has 

 made that the decisive year. He had until then marched 

 directly toward the promised land, but he had marched 

 backwards. As soon as he turned about, the whole of 

 his conquest appeared to him at once. 



VI 

 STUDIES OF 1867 



He began in fact the early experiments of 1867 with 

 clarified ideas, and also, which was not less important, 

 with means for work and experiment. The eggs which 

 he had prepared in 1865 and which had served for his 

 experiments of 1866 were not, as we have seen, wholly 

 freed from corpuscles. By raising them under special 

 conditions of cleanliness, by giving to his worms space 

 so that they would not infect each other, by isolating the 

 divers lots in separate baskets, by shiftings, that is to 

 say by removing the broods into the open air, all prac- 

 tices which, in his mind, were so many hygienic measures 

 as well as precautions against contagion, he had suc- 

 ceeded in having in 1866 a great number at least, if 

 not whole lots, of moths which were non-corpuscular, 



