CHAPTER VII 

 CHRONIC INFECTIOUS DISEASES 



Tuberculosis. — Tuberculosis is a chronic con- 

 tagious infectious disease of man and domestic 

 animals. It is characterised anatomically, in its 

 incipient stage at least, by small non-vascular nodules 

 known as tubercles, which have a tendency to undergo 

 cheesy degeneration. 



Etiology. — Koch's B. tuberculosis or one of its 

 varieties. 



Immunisation, — So far no practical attempt at 

 immunisation against tuberculosis has been made 

 in the lower animals with any success. Behring, in 

 1901, observing the varying pathogenic action of 

 human and bovine tubercle bacilli, declared that by 

 treating cattle with the less virulent human tubercle 

 bacilli they would be protected against the more 

 actively virulent bovine type, and thus also against 

 natural infection with tuberculosis. On the basis 

 of this assertion several methods of immunisation 

 for cattle have been recommended and actually 

 carried out in practice. However, satisfactory results 

 were not obtained except in cases where the most 

 strict hygienic and prophylactic measures were 



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