AETIOLOGY OF TUBERCULOSIS. 
71 
examination of the pictorial reproduction of prepared specimens with nucleus¬ 
coloring and illuminated by diffused light is concerned. 
As to the qualities of tuberculous bacilli in general, as they manifest themselves 
in the colored condition, the following is still to be mentioned. 
They always appear in the form of little staves whose length, as has already 
been given in the description of uncolored bacilli, is equal to 5 —£ of the diameter 
of a red blood corpuscle (about 0,0015—0,0035 mm). The diameter of the thick¬ 
ness is as constant as the length of the bacilli is variable, provided that one and 
the same coloring method is used. Under the coloring method first used by me, 
with alkaline methyline blue solution, they appear considerably thinner than with 
the use of Ehrlich’s method. It is difficult to fix the slight size relations about 
which we are here concerned without the use of photography. When I look 
through a considerable number of my bacteria photographs for bacilli which cor¬ 
respond best as to size with tuberculous bacilli, I find in F. Cohn’s “ Beitrage zur 
Biologie der Pflanzen,” II Vol., 3 Book, in the photographs given in Plate 15, No 
1 , among club-shaped bacilli with spores fixed in their ends, very thin and small 
bacilii which, if magnified 700 instead of 500 times as in the photograph, would 
come nearest to the tuberculous bacilli. There are among these bacilli also some 
which are spore-bearing and which about give a representation of the spore-bear¬ 
ing bacilli to be mentioned later. Also in the bacilli taken from blood putrefaction 
in mice (Miiuse septiciimie) and shown in this work, Yol. I, Plate VII, Fig. 41, are 
bacilli almost as thick, but on the average somewhat shorter than tuberculous 
bacilli. 
The tuberculous are usually not completely straight little staves; one usually 
finds slight breaks or bends and sometimes a crookedness which in the longest 
specimens goes so far as to suggest screwshaped windings. By this varying from 
the straight-lined forms the tuberculous bacilli distinguish themselves from other 
bacteria which come noticeably near them in size relations according to the photo¬ 
graphs. 
The distribution of the bacilli in the tuberculously-altered tissue is a very 
varying one. Sometimes they are heaped together in dense masses, so that by a 
very slight magnifying power bacilli-bearing spots can be recognized by their blue 
color. Very frequently, however, they are present only in small numbers. One 
finds the bacilli with most certainty where the tuberculous process is just beginning 
or is in a state of rapid growth. Here they are to be found in moderate numbers 
and between the nuclei of the cells which are heaped together and which usually 
show the epithelioid character at an early stage. After a more careful observation 
it is manifest that a bacillus almost always lies close beside a nucleus, and that it 
is to be found in the interior of the cell belonging to this nucleus. One cell can 
often contain two or even three bacilli. In places where the disease has made 
greater progress the number of bacilli usually increases extraordinarily. They 
theu often group themselves into little heaps closely pressed together, in which the 
bacilli lie parallel and are connected, so closely that it is often difficult to recognize 
the fact that the group is composed of single bacilli. In this arrangement the tuber¬ 
culous bacilli bear a great resemblance to the lepra bacilli, which are mostly grouped 
in this manner. The relation of the tuberculous bacilli to the cells cannot be de¬ 
cided in this stage, because the cells have already experienced great changes and 
