36 
SUMMARY. 
We have no easy method of determining the death of the tubercle 
bacillus; its virulence fades before it dies. The criterion of death 
depends upon animal experimentation. 
The tubercle bacillus may be classed with the nonspore-bearing 
organisms so far as its viability: is concerned. 
It is doubtful whether the waxy substance protects the bacillus 
against external harmful influences to any unusual extent. 
The thermal death point is 60° C. for twenty minutes. This is 
much less than was once considered. 
Further work upon the viability of the dried tubercle bacillus in 
dust, sputum, etc., may change our views as to its hardiness and 
danger under these conditions. 
The comparative short life upon artificial culture media contrasts 
strangely with the long life claimed for it under unfavorable condi- 
tions. 
Failure to recognize the lesions produced by the dead tubercle 
bacillus is responsible for some of the false conclusions reached by 
experimenters upon this subject. 
In all cases where the lesions in the test animal are doubtful, inoc- 
ulations into secondary animals are necessary to determine whether 
we are dealing with living or dead tubercle bacilli. 
