XI. 

 BACILLI IN CHRONIC INFECTIOUS DISEASES. 



IN tuberculosis, leprosy, glanders, and syphilis we have a group 

 of infectious diseases which present many points of resemblance. 

 All run 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 microorganism. 



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. 



This achievement, the result of patient and intelligent scientific 

 investigation, will always rank as one of the most important in the 

 history of medicine. The previous demonstration by Villemin (1865) 

 confirmed by Cohnheim (1877) and others that tuberculosis might 

 be induced in healthy animals by inoculations of tuberculous mate- 

 rial, had paved the way for this great discovery, and advanced 



