1894.] MICROSCOPICAL JOURNAL. 291 



able organism from 1.5 to 3.5 micromillimeters in length, 

 and about 0.2 of a micromillimeter in breadth. It is re- 

 cognized by its morphology and staining peculiarities, 

 the latter being so distinctive as to permit its ready dif- 

 ferentiation from all other bacteria, with but a single 

 known exception. 



The bacilli are found in the sputum of persons suffer- 

 ing from pulmonary and laryngeal tuberculosis ; in 

 miliiary tubercles and fresh caseous masses in the 

 lungs or elsewhere ; in recent tuberculous cavities in 

 the lungs ; and in the milk of a considerable per cent of 

 tuberculous cows. Except in the laboratory, where a 

 suitable pabulum,proper temperature and other surround- 

 ings are applied, the tubercle bacilli are incapable of liv- 

 ing a saprophytic form of existence, and therefore do not 

 multiply outside of the body of infected persons or ani- 

 mals, although many recent observations have shown 

 beyond cavil that they retain their vitality and virulence 

 for months and even years in rooms that have been in- 

 habited by tuberculous persons, particularly in crevices 

 and dark recesses, where they are protected from the 

 action of strong rays of light. Exposure to the direct 

 rays of the sun, however, destroys them, in a few minutes 

 or hours, according to the thickness of the layer of sputum 

 or other material with which they have been deposited, 

 while a bright diffused light also renders them inert after 

 a variable, but much longer time. The bacilli gain access 

 to the organism in some instances through the milk and 

 meat of infected animals, in which cases they are capa- 

 ble of setting up, in susceptible persons, especially in 

 children, tuberculosis of the bowels ; fresh wounds and 

 abraded surfaces also occasionally become inoculated > 

 but in the vast majority of cases their portal of entry is 

 through the respiratory organs, by the inhalation of dust 

 containing the bacilli or their spores. 



