AETIOLOGY OF TUBERCULOSIS. 
69 
of an enwrapping substance which joins them. It is therefore thinkable, that a 
coating exists, possessed with special properties, and enwrapping the bacilli, and 
that this allows the entrance of coloring matters under the simultaneous influence of 
alkali aniline and similar matters, but is on the contrary more or less impenetrable 
for acids. But in the-face of the facts now known, one cannot go farther than to 
conjectures. 
If I now go over to the description of the tuberculous bacilli themselves, although 
they were first made visible by the help of coloring matters, it appears nevertheless 
to the point, first to describe their properties as they make themselves known in a 
living condition and without being influenced by any sort of reagents. To get 
preparations for this sort of observation, only such tuberculous substances can be 
used as contain considerable masses of bacilli, because single bacilli cannot be distin¬ 
guished with certainty in the masses of detritus without help of the color reac¬ 
tion. For this purpose I have used little tuberculous knots from the lungs of 
guinea pigs, after I had convinced myself by coloring of the great quantity of 
tnberculous bacilli in them; the little knots were crushed in a drop of blood 
serum free from bacteria, the substance spread about as finely as possible in the 
liquid, a drop of this liquid sufficiently large for microscopic examination spread 
out flat on the under side of a covering-glass and fastened with vasiline on to a 
hollow object-holder, in order to avoid disturbing currents in the liquid and a too 
quick evaporation. In a preparation prepared in this manner, in the microscopic 
examination conducted in the usual manneiythat is to say in a suitable “ab- 
blendung” of the light by diaphragms, there are found among opaque heaps of in¬ 
determinable nuclei, brighter spots in which the formed elements lie less thickly, 
and here one notices numerous colorless, very fine and short little staffs. The 
same are mostly united in small groups; in those which lie singly aside from the 
so-called molecular motion, no motion of their own is to be noticed. The length 
of the little staffs is about from one-quarter to one-half of the diameter of a red 
blood corpuscle. An organization is not be noticed in them, and one cannot re¬ 
organize their relations to the surrounding cells in this sort of examination, and 
if no farther observations could be made, one would rather believe he had some 
sort of lifeless forms before him than bacteria. 
If such a covering-glass be lifted up from the concave object-holder, so that 
the bacilli-bearing substance be dried and then doubly dyed in the manner already 
described, then the numerous grains and remains of cells appear dyed brown, 
the little staffs on the contrary receive an intense blue coloring and distinguish 
themselves sharply from all known component parts of the animal tissue with 
which they are mixed. The bacilli do not show themselves in their full number 
until after their coloring; they may be distinguished not only on the thinnest 
spots of the preparation, but everywhere with full certainty, even among the 
thick heaps of cells. It is noticeable that the little staffs appear thinner after 
the coloring than in the uncolored condition, the reason for which is, that be¬ 
fore the coloring they must be observed by light cut off by diaphragms, in which 
case the lines of interference on the borders of the object appear to enlarge its 
diameter, while the observation of the colored bacilli is made in full light falling 
upon it from all sides, through which all phenomena of interference are ex¬ 
cluded. 
