CHAPTER IX. 



TUBERCULOSIS. 



THE cause of tubercle was proved by Koch in 1882 to be the 

 organism now universally known as the tubercle bacillus. 

 Probably no other single discovery has had a more important 

 effect on medical science and pathology than this. It has not 

 only shown what is the real cause of the disease, but has also 

 supplied infallible methods for determining what are tubercular 

 lesions and what are not, and has also given the means of 

 studying the modes and paths of infection. A definite answer 

 has in this way been supplied to many questions which were 

 previously the subject of endless discussion. 



Historical. By the work of Armanni and of Cohnheim and Salomonsen 

 (1870-80) it had been demonstrated that tubercle was an infective disease. 

 The latter observers found on inoculation of the anterior chamber of the 

 eye of rabbits with tubercular material that in many cases the results of 

 irritation soon disappeared, but that after a period of incubation, usually 

 about twenty-five days, small tubercular nodules appeared in the iris ; 

 afterwards the disease gradually spread, leading to a tubercular disorgan- 

 isation of the globe of the eye. Later still, the lymphatic glands became 

 involved, and finally the animal died of acute tuberculosis. The question 

 remained as to the nature of the virus, the specific character of which 

 was thus established, and this question was answered by the work 

 of Koch. 



The announcement of the discovery of the tubercle bacillus was made 

 by Koch in March 1882, and a full account of his researches appeared in 

 1884 (Mitth. a. d. K. Gsndhtsamte., Berlin). Koch's work on this subject 

 will remain as a classical masterpiece of bacteriological research, both on 

 account of the great difficulties which he successfully overcame and the 

 completeness with which he demonstrated the relations of the organism 

 to the disease. The two chief difficulties were, first, the demonstration 

 of the bacilli in the tissues, and, secondly, the cultivation of the organism 

 outside the body. For, with regard to the first, the tubercle bacillus 

 cannot be demonstrated by a simple watery solution of a basic aniline 

 dye, and it was only after prolonged staining for twenty-four hours, with 

 a solution of methylene-blue with caustic potash added, that he was 

 able to reveal the presence of the organism. Then, in the second place, 



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