TUBERCULOSIS IN ANIMALS. 237 



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 dis- 

 appeared, 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 disorganisation of the globe of the eye. Later, 

 the lymphatic glands became involved, and finally the animal died of acute 

 tuberculosis. The question remained as to the nature of the virus, the spe- 

 cific 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 re- 

 main 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, all attempts to cultivate it on the ordinary media failed, and he 

 only succeeded in obtaining growth on solidified blood serum, the method of 

 preparing which he himself devised, inoculations being made on this medium 

 from the organs of animals artificially rendered tubercular. The fact that 

 growth did not appear till the tenth day at the earliest, might easily have led 

 to the hasty conclusion that no growth took place. All difficulties were, how- 

 ever, successfully overcome. He cultivated the organism by the above method 

 from a great variety of sources, and by a large series of inoculation experiments 

 on various animals, performed by different methods, he conclusively proved 

 that bacilli from these different sources produced the same tubercular lesions 

 and were really of the same species. His work was the means of showing 

 conclusively that such conditions as lupus, "white swelling" of joints, scrofu- 

 lous disease of glands, etc., are really tubercular in nature. 



Tuberculosis in Animals. Tuberculosis is not only the most 

 widely spread of all diseases affecting the human subject, and 

 produces a mortality greater than any other, but there is proba- 

 bly no other disease which affects the domestic animals so widely. 

 We need not here describe in detail the various tubercular lesions 

 in the human subject, but some facts regarding the disease in 

 the lower animals may be given, as this subject is of great im- 

 portance in relation to the infection of the human subject. 



Amongst the domestic animals the disease is commonest in cattle (bovine 

 tuberculosis), and in them the lesions are very various, both in their character 



