TUBERCULOSIS. 211 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 flagella. 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.