264 BACTERIOLOGY. 
The bacilli are found in the sputum of persons suf- 
fering from pulmonary or laryngeal tuberculosis, either 
free or in the interior of pus-cells; in miliary tubercles 
and fresh caseous masses in the lungs and elsewhere; 
in recent tuberculous cavities in the lungs; in tuber- 
culous glands, joints, bones, mucous membranes, and 
skin affections; in the lungs of cattle suffering from 
pulmonary tuberculosis, and in tubercular nodules, 
generally in animals which are infected naturally or 
by experimental inoculations. 
Morphological Characters. The tubercle bacilli are 
slender, non-motile rods of about 0.2” in diameter by 
1.5 to 4u in length. (Plate I., Figs. 1, 2, and 3.) 
Commonly they occur singly or in pairs, and are then 
usually slightly curved; frequently they are observed 
in smaller or larger bunches. Under exceptional con- 
ditions branching forms are observed. In stained 
preparations there are often seen unstained portions, 
which have been improperly thought to be spores. 
From two to six of these unstained spaces may some- 
times be noticed in a single rod, and under moderate 
magnification may give to the bacilli the appearance 
of short chains of streptococci. - In old cultures irregu- 
lar forms may be obtained, the rods being occasionally 
swollen at one end or presenting lateral projections. 
The staining peculiarities of this bacillus are very 
important, for by them its differentiation and recogni- 
tion in microscopical preparations of sputum, etc., are 
rendered possible. It does not readily take up the 
ordinary aniline colors, but when once stained it is 
very difficult to decolorize, even by the use of strong 
acids. Koch first recognized it in a staining prepara- 
tion to which an alkali had been added—a solution of 
