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degree of virulence, which is fatal to only the 

 weakest birds, up to a deadly form which sweeps away 

 anything and everything in the shape of a cage bird 

 that is exposed to the infection, and that is not 

 individually either wholly or partially immunized 

 against it ? 



Now let us see how an epidemic of Septic Fever 

 can spontaneously occur. The case I cite happened 

 in Dr. Clarke's own personal experience, and the 

 evidence is therefore that of an observer trained in 

 those logical methods that alone are of any value in 

 the investigation of pathological problems. Some 

 years ago he had a garden aviary put up for his wife, 

 which was built so as to ensure constant fresh air to 

 the inmates, and which was kept under the most 

 scrupulous conditions of cleanliness. For some time 

 previous to 18S7, when the following occurrences 

 took place, and also during that year, no fresh bird 

 had been admitted to the establishment ; therefore we 

 can eliminate the possible factor of infection having 

 been brought in from the outside. Towards the end 

 of the breeding season the birds began to drop off in a 

 a mysterious fashion : Mrs. Clarke sent for a veterinary 

 surgeon — an expert in birds — who came and examined 

 them, took away some dead bodies for autopsy, and in 

 due course sent in his report, diagnosing tuberculosis. 

 Dr. Clarke, who at the time was specially engaged in 

 original research in this disease, was naturally glad to 

 embrace so favourable an opportunity of studying 

 what seemed to be a spontaneous outbreak of the 

 avian variety, and therefore took down, to the 

 laboratory where he was then working, some of the 

 dead bodies for the purpose of making cultures and 

 microscopic slides. To his great surprise the enlarged 

 and nodulated spleens and livers yielded no tubercle 

 bacilli, though of the various forms of the septic 

 bacterium there were more than enough in the 



