II. THE VIABILITY OF THE TUBERCLE BACILLUS. 
By M. J. Rosenau, 
Director Hygienic Laboratory , United States Public Health and Marine- Hospital Service , 
Washington , D. C. 
Practically all observers agree with Koch that human sputum is 
the main source of human tuberculosis. Whether the tubercle 
bacillus is usually transferred directly or indirectly, in moist or in 
dry state, by inhalation or ingestion, are questions still at issue. 
The viability of the tubercle bacillus, therefore, assumes a special 
significance in aiding the solution of problems concerning the channels 
of infection and methods of transmission of this disease. Further, a 
correct understanding of the vitality of the tubercle bacillus is of 
first importance in carrying out many of our prophylactic measures. 
No one questions that many of the tubercle bacilli are still alive 
and virulent in the droplets that are sprayed from the mouths of 
consumptive persons. Likewise many of the bacilli must be fresh 
and active when deposited by consumptives upon drinking cups, 
spoons, towels, or other articles mouthed by well persons shortly after- 
wards and without intervening cleansing. Whether the bacilli remain 
alive and virulent in dried and pulverized sputum in sufficient num- 
bers to frequently form a dangerous part of the dust of rooms and 
streets is a question still open for solution. 
Two principal destructive agencies act on the tubercle bacillus in 
sputum expectorated on streets and out-of-door places: (1) Desic- 
cation and (2) the action of light. The bacillus also has to contend 
with other destructive agencies, such as the putrefactive and other 
organisms in the sputum or gaining access to it. 
THE TUBERCLE BACILLUS AND ITS SUPPOSED SPORE. 
Koch at first believed that the tubercle bacillus contained spores. 
He was led into this error by the beaded appearance of the rod. We 
now know that the tubercle bacillus does not possess an endogenous 
spore, such as that of the anthrax bacillus, the tetanus bacillus, or 
the hay bacillus. 
( 25 ) 
