152 PASTEUR: THE HISTORY OF A MIND 



peared should be the most robust, the disease seemed 

 to be epidemic, and on account of its slow and regular 

 progress, from our country toward the most distant 

 regions of Europe and Asia, it seemed to present in 

 the highest degree the contagious character: and yet 

 other facts, not less numerous, and not less convincing 

 in appearance, bore witness that it was neither epidemic 

 nor contagious. I will cite only one of them, which 

 Pasteur had learned at the beginning of his studies, 

 and which had troubled him somewhat. In the culture 

 of a mixture of two "graines, " the one giving white 

 cocoons and the other yellow ones, it had been observed 

 that the first died almost completely, while the other 

 gave a very satisfactory harvest. 



The uncertainty was not less great if one sought to 

 study the disease by itself, without being preoccupied 

 any more with its nosological character. Thus, de 

 Quatrefages, after having made a careful study, believed 

 himself able to characterize it by the existence in the 

 interior and especially upon the skin of the worm, of very 

 small spots resembling grains of black pepper, and for this 

 reason had been led to name it pebrine. But experiment 

 showed that the worms could be spotted without being 

 sick, and on the other hand that worms which were 

 not spotted did not necessarily give good eggs. If one 

 wished to enter further into the study of the disease, 

 he found himself in the presence of contradictory results 

 obtained by various physiologists. For example, Lebert 

 and Frey had established that in the interior of all the 

 diseased worms and all the diseased moths there existed 

 in abundance a peculiar parasite, the corpuscle, visible 

 only under the microscope, observed for the first time 

 by Gue'rin-Meneville, and the importance of which 

 from the pathological point of view had been caught sight 

 of by Cornalia. But if one believed Philippi, another 



