MYCOBACTERIACE^: THE TUBERCLE BACILLUS 32 1 



If this occurs early the bacilli may be entirely destroyed and the 

 abnormal tissue may disappear completely or remain only as a 

 little hyaline or fibrous tissue. After caseation has occurred, 

 healing results in the formation of a dense fibrous nodule, usually 

 with calcareous material in the center, in which living tubercle 

 bacilli can usually be demonstrated. 



The mode of infection in human tuberculosis has been a matter 

 of some controversy and much of the evidence concerning it 

 has been derived from animal experimentation. Unquestionably 

 tubercle bacilli may pass through epithelial surfaces, especially 

 of mucous membranes, without production of any demonstrable 

 lesion. Ingested bacilli readily pass through the intestinal 

 mucosa, especially during the digestion of fat, and they may ' 

 first produce lesions" in the mesenteric lymph glands, the liver 

 or in the lungs. In the latter instance, they doubtless pass with 

 the absorbed fat thrpugh the thoracic. duct, superior vena cava 

 and right heart to the pulmonary arteries. In man, the most 

 important mode of infection is through inhaling the dust of dry 

 powdered sputum, as a result of which lesions develop in the 

 lungs. Tuberculosis may occur in any tissue of the body, reach- 

 ing it through the blood and lymph. A massive infection of 

 the blood stream often leads to generalized miliary tuberculosis 

 with minute tubercles in all the organs. 



The bacteriological diagnosis of the disease depends upon 

 finding the tubercle bacilU in discharges from the suspected 

 lesion. In sputum an acid-proof bacillus of the proper size and 

 shape is almost invariably a tubercle bacillus and a diagnosis 

 based upon such a finding by an experienced microscopist is 

 justly regarded as very accurate. Inoculation of guinea-pigs 

 will clinch the proof. The latter procedure will also sometimes 

 detect tubercle bacilli when careful microscopic search has failed. , 

 In discharges from the intestine or urinary organs one may 

 meet with other acid-proof organisms (5. smegmatis), and more 

 care is necessary in arriving at a diagnosis. In tuberculous 

 meningitis, the tubercle bacillus may be detected by. microscopic 



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