TUBERCULOSIS 117 



such studies of degeneration of lung tissue Laennec'thus 

 showed that consumption and tubercle were nothing 

 more than parts of the same situation. 



COMMUNICABILITY OF TUBERCULOSIS. No one ap- 

 parently believed in the possibility of tuberculosis being 

 a communicable disease until the epoch-making studies 

 of Villemin, who in 1862 demonstrated by carefully con- 

 trolled animal experimentation that tuberculosis could 

 be communicated from one animal to another, thus for 

 the first time refuting the existing theory that tubercu- 

 losis was a hereditary disease. 



THE TUBERCLE BACILLUS. The causative agent of 

 tuberculosis was not known until in 1882 Koch of Berlin 

 described the tubercle bacillus. Not until 1884 did he 

 fully describe the nature of this parasite and show that 

 the tubercle bacillus was found in tuberculosis of the 

 lungs; in " white swellings" which some authorities be- 

 lieved to be tuberculosis; in Pott's Disease; in diseases 

 of the hip; and in lupus (tuberculosis of the skin). He 

 showed also that this organism, which was always pres- 

 ent in these various conditions, could be grown arti- 

 ficially in various media in pure culture; that the pure 

 culture would show no parasitic life other than the 

 tubercle bacillus; that when these tubercle bacilli were 

 introduced into animals they reproduced a disease 

 identical in its lesions to the disease known as tubercu- 

 losis; and finally that these same tubercle bacilli could 

 be recovered from the organs of the animal which had 

 been given the disease. 



How Do THE BACILLI ENTER THE BODY? As soon 

 as Koch's epoch-making discoveries were made known 



