HISTORY OF RESEARCH ON TUBERCLE. 225 



also from experimental results. Investigators who repeated Villemin's 

 experiments obtained similar results so far as the production of 

 tuberculosis by tubercular material was concerned, but many found 

 that tuberculosis also followed inoculation with non-tubercular material 

 (such as pus from pysemic abscesses, portions of decomposed tissue, 

 etc.), and even by the mere introduction of setons. The general 

 opinion came to be strongly against the existence in tubercle of an 

 infective agent of specific nature, and along with this there prevailed 

 great confusion as to the distinction between tubercular and non- 

 tubercular lesions. 



Armanni, in 1873, by scarification of the cornea and inoculation 

 with tubercular material, produced in that situation a small tubercular 

 ulcer, which was afterwards followed by general tuberculosis. Such a 

 result he found never followed inoculation with non-tubercular material. 

 But it was the work of Cohnheim and Salomonsen along similar lines 

 which was chiefly instrumental in altering the prevailing opinion as 

 to the nature of tubercle. By inoculation of the anterior chamber 

 of the eye of rabbits with tubercular material they found 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 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 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 master-piece 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 



