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and death frequently supervenes after a dumb agony, before 

 the animal has stirred from its place ; sometimes there is a 

 faint fluttering of the wings for a few seconds." 



Pasteur tried the effect of this microbe on guinea-pigs which 

 had been brought up in the laboratory, and found it but rarely 

 mortal; in general it merely caused a sore, terminating in an 

 abscess, at the point of inoculation. If this abscess were 

 opened, instead of being allowed to heal of its own accord, the 

 little microbe of chicken cholera was to be found in the pus, 

 preserved in the abscess as it might be in a phial. 



"Chickens or rabbits," remarked Pasteur, "living in the 

 society of guinea-pigs presenting these abscesses, might sud- 

 denly become ill and die without any alteration being seen in 

 the guinea-pigs' health. It would suffice for this purpose that 

 those abscesses should open and drop some of their contents 

 on the food of the chickens and rabbits. 



" An observer witnessing those facts, and ignorant of the 

 above-mentioned cause, would be astonished to see hens and 

 rabbits decimated without apparent cause, and would believe 

 in the spontaneity of the evil ; for he would be far from sup- 

 posing that it had its origin in the guinea-pigs, all of them in 

 good health. How many mysteries in the history of con- 

 tagions will one day be solved as simply as this 111" 



A chance, such as happens to those who have the genius of 'N 

 observation, was now about to mark an immense step in 

 advance and prepare the way for a great discovery. As long 

 as the culture flasks of chicken-cholera microbe had been sown 

 without interruption, at twenty -four hours' interval, the 

 virulence had remained the same ; but when some hens were 

 inoculated with an old culture, put away and forgotten a few 

 weeks before, they were seen with surprise to become ill and 

 then to recover. These unexpectedly refractory hens were 

 then inoculated with some new culture, but the phenomenon 

 of resistance recurred. What had happened? What could 

 have attenuated the activity of the microbe ? Researches 

 proved that oxygen was the cause ; and, by putting between 

 the cultures variable intervals of days, of one, two or three 

 months, variations of mortality were obtained, eight hens dying 

 out of ten, then five, then only one out of ten, and at last, 

 when, as in the first case, the culture had had time to get stale, 

 no hens died at all, though the microbe could still be cultivated. 



"Finally," said Pasteur, eagerly explaining this pheno- 



