XII. 
BACILLI IN CHRONIC INFECTIOUS DISEASES. 
In tuberculosis, leprosy, glanders, and syphilis we have a group 
of infectious diseases which present many points of resemblance. 
Allrun a chronic course; all may be communicated to susceptible 
animals by inoculation ; in all, the lymphatic glands in the vicinity 
of the point of inoculation become enlarged, and new growths, con- 
sisting of various cellular elements of a low grade of vitality, are de- 
veloped in the tissues which are the point of predilection for each ; 
in all, these new growths show a tendency to degenerative changes, 
as a result of which abscesses, caseous masses, or open ulcers are 
formed. 
In two of the diseases in this group—tuberculosis and glan- 
ders—the infectious agent has been obtained in pure cultures and its 
specific pathogenic power demonstrated by inoculations in susceptible 
animals; in one—leprosy—there is but little doubt that the bacillus con- 
stantly found in the new growths characteristic of the disease bears 
an etiological relation to it, although this has not been demonstrated, 
the bacillus not having as yet been cultivated in artificial media. 
The evidence with reference to the parasitic nature of the fourth dis- 
ease mentioned as belonging to this group—syphilis—is still unsatis- 
factory, but there is every reason to believe that it will also eventu- 
ally be proved to be due to a parasitic microérganism. 
The announcement of the discovery of the tubercle bacillus was 
made by Koch, in March, 1882, at a meeting of the Physiological 
Society of Berlin. At the same time satisfactory experimental evi- 
dence was presented as to its etiological relation to tuberculosis in 
man and in the susceptible lower animals, and its principal biologi- 
cal characters were given. 
Baumgarten independently demonstrated the presence of the tu- 
bercle bacillus in tuberculous tissues and published the fact soon 
after the appearance of Koch’s first paper. The previous demonstra- 
tion by Villemin (1865)—confirmed by Cohnheim (1877) and others— 
that tuberculosis might be induced in healthy animals by inocula- 
tions of tuberculous material, had paved the way for his discovery, 
