ETIOLOGY OF TUBERCULOSIS. 
127 
solution. When the bacteria to be cultivated are spread out upon the stiffened 
serum, just up to the edge of this liquid, then they develop at the same time and 
close by each other on the firm breeding ground and in the breeding liquid, so 
that their special modes of growth in liquid and upon a firm substratum can be 
immediately compared. 
When the re-agent glasses provided with stiffened blood serum are preserved 
for a length of time, since the wadding stopper does not prevent evaporation of 
the moisture, a very gradual drying of the serum, progressing from above down¬ 
wards, takes place, yet it occurs so slowly that for months a sufficiently large area 
suitable for cultures remains at disposal between the upper dried part of the serum 
and the lower part covered by the liquid. 
When the sterilization of the blood serum has not succeeded, this shows itself 
a few days after the stiffening, especially if the serum be put experimentally into 
the breeding apparatus. In these cases little whitish points form which appear 
singly or in larger numbers, and soon enlarge. Sometimes the blood serum becomes 
liquid under the influence of such bacteria, then loses its clearness and becomes 
covered with a whitish skin. Microscopic investigation shows that we here always 
have bacilli which plainly have proceeded from spores germinating late. As a 
matter of course, only such serum glasses may be used for ‘ ‘ reinculturen ” as after 
several days’ stay in the breeding apparatus show no trace of such impurities, but 
remain completely clear and transparent. For many purposes, especially when it 
is wished to examine the reinculturen directly with the microscope under slight 
magnifying power, it is to the purpose to stiffen the serum in watch glasses or 
other suitable vessels. Such vessels should have a glass cover as a protection 
against the entrance of air germs. They are further placed in glass vessels which 
are lined with moist blotting paper, and can so be exposed to the breeding temper¬ 
ature. So sure a protection from inj urious impurities as the re-agent glasses closed 
by wadding is, to be sure, not given by this arrangement, and reinculturen con¬ 
tinued through many repeated breedings of tuberculous bacilli are only to be carried 
on by the help of blood serum stiffened in the re-agent glasses. 
Just as great care as the preparation of the sterilized stiffened blood serum 
demands is absolutely necessary when the sowing is to be made on the prepared 
breeding ground, if at the same time the entrance of foreign germs and the defile¬ 
ment of the breeding ground by bacteria and fungi is to be prevented. 
As to the material to be used for sowing, that is naturally the most suitable 
which contains many bacilli, is of a soft nature (that the bacilli may be spread as 
quickly as possible), and is as fresh as possible, that is as free from the bacteria of 
decay. When these latter are confined to the surface of the organ which is to serve 
as a point of departure for culturen, it is still possible with certain precautions to 
obtain reinculturen of tuberculous bacilli. But as soon as the foreign bacteria 
have forced themselves into the deeper layers all attempts to separate the tubercu¬ 
lous bacilli from them in culturen will be in vain, because the bacteria of decay 
grow with extraordinary rapidity in comparison with tuberculous bacilli and 
have taken possession of the entire breeding ground before the last have reached 
a visible growth. 
Also, when the sowing material contains very few bacilli and is of a firm con¬ 
sistence, there are difficulties in causing the cultures to grow. In this case, namely, 
