252 TUBERCULOSIS. 



in the tubercle bacillus. Koch proved incontrovertibly 

 in 1882 that it alone can produce tuberculosis. Koch 

 also showed that the bacillus may be cultivated outside 

 of the human body in an artificial nutriment (best in 

 blood serum, coagulated by heat or nutrient agar, to 

 which five percent glycerine has been added), and finally 

 that in suitable climates tuberculosis may be produced 

 by inoculation with pure cultures. He found the bacil- 

 lus constantly present in thirty-three cases of tubercu- 

 losis in men, and in thirty-four cases in animals, and in 

 three cases of scrofula in men. He had by its means 

 produced experimental tuberculosis in 174 guinea pio:s, 

 thirty-two rabbits and five cats. He had subjected his 

 discovery to every crucial test. From this time on the 

 bacillus tuberculosis has been the subject of earnest 

 work of all students of general bacteriology and experi- 

 mental medicine. It is a minute, rod-shaped vegetable 

 organism, varying from l.S™"" to 3.5""^ in length, and 

 0.2°''" in breadth. It is easily recognized by its staining 

 peculiarities, differing from all oxher bacteria except 

 that of leprosy. 



Except in proper cultures in favorable temperatures, it 

 does not multiply outside infected persons or animals, 

 although it has been proven that it will retain vitality 

 and virulence for months, and" even years in dark rooms 

 that have been occupied by tuberculous patients. The 

 bacillus or little rod is so minute that it is practically 

 imjDossible to see it unless it is brought into contrast 

 with its surroundings by staining it and leaving the 

 back ground unstained or mce 'oersa. One method is 

 to color the whole mass with a saturated alcoholic 

 solution of fuchsin and then by immersion in 

 dilute nitric acid the color is abstracted from the 

 surrounding substances, leaving the tubercle bacilli 

 standing out as little rods on a colorless ground. When 

 the world accepted Koch's theory of the bacillary origin 



10O 



