STUDIES OF 1865 155 



there were two cultures of silkworms, two broods (deux 

 chambre'es): the one finished and ascended to the 

 heather, the other coming out of the fourth molt. The 

 first had gone along admirably. The worms had climbed 

 up all at one time, and appeared so vigorous that they 

 were preparing to make use of all the cocoons for the 

 egg-laying. The second had dragged along, and presented 

 a bad appearance; the worms were languishing, ate little, 

 and did not grow. The sequel proved that this appear- 

 ance was not deceptive: the harvest of cocoons was 

 almost a failure. 



Now, on examining with the microscope the chrysalids 

 and the moths of the culture which had succeeded well, 

 corpuscles were found everywhere in them, while there 

 were corpuscles only exceptionally in the worms of the 

 bad brood. And this was not an exceptional fact, for, 

 by searching in the neighborhood, Pasteur found a mul- 

 tiplicity of similar cases. 



What did this mean? The corpuscles and the disease 

 of silkworms were, therefore, two distinct things. Could 

 worms be very healthy and behave properly, like the 

 worms of the first culture, and nevertheless give cor- 

 puscular chrysalids? Could they be sick, like the worms 

 of the second, and not contain corpuscles? To-day we 

 know that if Pasteur did not find out this it was because 

 he investigated badly, confounding in his inexperience 

 two diseases. There is one in which the corpuscle plays 

 a r61e, another in which it does not. But Pasteur did 

 not know this, having only discovered it later. And, in 

 the meantime, the disturbing and imperious question 

 confronted him: what conclusion is to be drawn from the 

 preceding observation? 



In order to decide, it was prudent to wait and see what 

 would become of the cocoons of the bad brood. In fact, 

 in studying them day by day, as they developed, Pasteur 



