392 
ROBERT KOOH. 
EXPERIMENTAL PATHOLOGY, 
DIE (ETIOLOGY DER TUBERCULOSE (ETIOLOGY OF TUBERCULOSIS). 
. By Robert Koch.* 
In a first series of researches, the author has tried to find the 
parasitic cause of tuberculosis. After satisfying himself of the 
deficiency of the coloring processes in use for histological e e- 
ments, he accomplished positive results by the following method : 
The microscopic preparation is placed in a coloring solution ma e 
of 200 grammes of distilled water, mixed with one cubic centi¬ 
meter of a concentrated alcoholic solution of the blue of rnetliy 
line to which are then added two cubic centimeters of an alkaline 
liquid, for instance, of potash to the tenth. This mixture must 
not make any precipitate, even after several days’ rest. They 
are afterwards placed in a concentrated and filtrated solution o 
vesuvine, and left in it from two to twenty minutes, whether it is 
a piece of glass upon which has been stretched and-dyed a prep¬ 
aration in a fresh state, or, on the contrary, a section hardened in 
alcohol. The preparation is washed with distilled water, tie 
excess of water is removed with alcohol, and the preparation 
cleared off with the essence of clover. The specimens, can then 
be immediately examined or mounted. 
The treatment with the vesuvine has for its object-to remove 
from the preparation the excess of blue coloration coming fiom 
that of rnetliy line to transform this, saturated in a slightly brown¬ 
ish blue. . i , 
If this method is carefully followed, all the histological ele¬ 
ments, especially the nuclei and their products of desegiegation, 
appear brown under the microscope, while the tuberculous 
bacteria are of a handsome blue. The contrast is such that these 
are easily distinguished, even when in small numbers and apart. 
Koch has tried this mode of coloration upon a great number 
of other bacteria, and all are tinted brown, except those of lepra, 
which has a strong resemblance to those of tuberculosis. How¬ 
ever, the leprous bacteria are finer, pointed at their extremities, 
* Berlin Klin. Wochens. 
