158 PASTEUR: THE HISTORY OF A MIND 



the air he must indeed go haphazard, and the least 

 check discourages. The idea of Pasteur had, on the 

 contrary, an experimental foundation, and any one 

 could trust him when he followed an idea proceeding 

 from experiment. Ordinarily he distinguished very 

 quickly whether a thing was true or false. 



IV 

 STUDIES OF 1866 



However, in the subject under consideration, Pasteur 

 continued to deceive himself during the whole of the 

 year 1866, in consequence of a defect of technique which 

 we must notice. He had had at heart to apply himself 

 his method of egg-selection in order to procure mate- 

 rials for study the following year. He had, therefore, 

 sought in the vicinity of Alais chrysalids and moths 

 as healthy as possible. But the country was thoroughly 

 infected; moreover, the cultures were far advanced in 

 that place, and for the greater part had been used for 

 the spinning. It was with great difficulty that he could 

 procure a few cocoons derived from a culture in appear- 

 ance quite healthy and successfully completed. He 

 brought them to Paris to obtain their eggs. 



In the passage which I have just transcribed, Pas- 

 teur says that one opens the male and female to seek 

 therein the corpuscles. They proceeded at that time by 

 removing with scissors a part of the skin of the abdomen: 

 they spread out this shred upon a glass slide, scraped off 

 a little of the adipose cellular tissue which was brought 

 away with it, and examined this fragment after having 

 compressed it under a cover-glass. It was only later 

 that the moth was ground up in a mortar to study a 

 drop of the pap under the microscope. This slight 



