AETIOLOGY OF TUBERCULOSIS. 
149 
place, they never liquify the serum, as some sorts of bacteria regularly do. They 
do not penetrate into the serum, but always remain on its surface and lie loosely 
there. In consequence of this the membrane-like bacilli vegetation can be lifted 
and washed away by tipping the re-agent glass so that the liquid at its base may 
flow over the surface of the serum. Other bacteria possess a pap-like consistence 
and let themselves mingle with the liquid, making them cloudy. This is not the 
case with tuberculous bacilli. The thin membranes formed by them do not dis¬ 
solve in the liquid, but in consequence of their firm consistence break into larger 
or smaller lumps, which are washed away by the liquid, and finally collect at the 
bottom of the same. The peculiar stiff and brittle constitution of the colonies 
shows itself best in the part of the “ cultur” which covers over the liquid in the 
re-agent glass. As soon as this liquid is set in motion the little skin on its sur¬ 
face breaks into plates and lumps, which slowly sink to the bottom. The liquid 
always remains clear, as well when the bacilli vegetation itself stretches over it, as 
when by washing off of the serum surface masses of bacilli get into it, or when 
in the beginning the inoculating substance is intentionally put into it. From this 
appearance also we should conclude, as direct observation had already shown, that 
the tuberculous bacilli possess no independent motion; for bacilli which can move 
disperse themselves in all directions through the breeding solutions, and give them 
a cloudy appearance. 
Within certain limits, moreover, the conduct of the bacilli “ culturen,” as 
seen by the naked eye, depends upon the consistence of the blood serum upon 
which they grow. The firmer that is, the more the bacilli colonies have the con¬ 
stitution just described. On a very soft gelatinous serum the development is 
somewhat different. The distribution of the bacilli is not uniform because the 
hard and firmly coherent masses of bacilli cannot be crushed on the soft serum in 
the sowing. The inoculating substance therefore remains lying on the serum in 
small detached crumbs. The growth of the colonies does not reach so uniformly 
over the surface as on the firm serum, but leads to thicker compact masses which 
cling firmly to the soft serum. Even when the serum is somewhat less soft, so 
that the colonies begiu to spread themselves out on the surface, one notices a 
firmer attachment of the bacilli membrane to the serum area. One does not 
then succeed in washing the membrane from the serum, or lifting it off with the 
platinum wire, without at the same time loosening parts of the serum. 
When even the properties of the “ culturen ” noticeable with the naked eye 
show a difference from other bacteria and admit a judgment as to their purity, 
this is much more the case when they are examined under a moderately strong 
magnifying power, such as is obtained with Zeiss’ Objective System, A. A., ocular 
4, with drawn out tube, (80 fold magnifying power). It is then seen that the 
bacilli colonies form such peculiarly shaped figures as do no other sort of bacteria. 
Microscopically of course these colonies can be noticed far earlier than with the 
naked eye. Already five to six days after the sowing takes place and the “ cul¬ 
tur ” has been kept at breeding warmth, peculiar, very dainty little figures appear 
on the surface of the serum. These appear as fine lines, often bow-shaped. The 
smallest have mostly the figure of an S. Longer colonies show the most manifold 
serpentine turns and windings which often remind one of interlacing letters. 
While the ends of these lines run off into sharp points, in the middle they are 
