all known spores resist lieat more strongly than the fully-
developed bacilli, bnt experimentation has shown that
these degenerative forms are no more capable of resist-
ing heat than the tubercle bacilli themselves.
The organism is not motile, and does not possess
The tubercle bacillus is peculiar in its reaction to the
anilin dyes. It is rather difficult to stain, requiring that
the dye used shall contain a mordant (Koch), but it is also
very tenacious of the color once assumed, resisting the
decolorizing power of strong mineral acids (Ehrlich).
These peculiarities delayed the discovery of the bacil-
lus for a considerable time, but now that we are familiar
with them they give us a most valuable diagnostic cha-
racter, for with the exception of the bacillus of lepra no
known bacillus reacts in exactly the same way.
Koch first stained the bacillus with an aqueous solu-
tion of a basic anilin dye to which some potassium
hydrate was added, subsequently washing with water
and counter-staining with vesuvin. Ehrlich subsequently
modified Koch's method, showing that pure anilin was
a better mordant than potassium hydrate, and that the
use of a strong mineral acid would remove the color
from everything but the tubercle bacillus. This modi-
fication of Koch's method given us by Ehrlich is at the
present time acknowledged to be the best method of
staining the bacillus. Many other methods have been
suggested, all of them, perhaps, more convenient than
Ehrlich's, but none so good.
As being that most frequently performed by the
physician, we will first describe the method of seeking
the bacillus in sputum.
If one desires to be very exact in his examination,
it may be well to have the patient cleanse the mouth
thoroughly upon waking in the morning, and after the
first fit of coughing expectorate into a clean wide-
mouthed bottle. The object of this is to avoid the
presence of fragments of food in the sputum.