TUBERCLE BACILLUS 467 
l)elieve(l that the deeply stainino; granules found in the bacillus might 
be true endospores. The generally accepted view is opposed to this 
supposition.^ 
Staining.— Tubercle bacilli and closely related organisms possess 
in common a relatively large amount of waxy substance- which is 
relatively impervious even to the more intense stains, as carbol-fuchsin. 
Ordinary anilin dyes do not stain members of the tubercle bacillus 
group. They are Gram-positive, but it requires several hours for the 
anilin-oil gentian violet to color the organisms. When a stain has 
penetrated the substance of the tubercle bacillus it is retained with 
great tenacity; alcohol and even mineral acids in moderate concen- 
tration fail to remove it except after long exposure. The members 
of the tubercle bacillus group vary somewhat in this resistance to 
decolorization ; the true tubercle bacilli are both "alcohol-" and 
"acid-fast;" other organisms in the group may be either "alcohol-" 
or "acid-fast." Young tubercle bacilli are frequently non-acid-fast.^ 
Fig. 66. — Tubercle bacilli, beaded forms. 
The best and most universally applicable stain for the tubercle 
bacillus is the Ziehl-Xeelsen stain. "* It is used as follows: 
1. A thin smear of the material to be examined for tubercle bacilli 
is prepared and fixed in the usual manner, then flooded with carbol- 
fuchsin and steamed gently (not boiled) for five minutes. The pre- 
paration must be flooded continuously with the stain. 
' See Wherry (Centralbl. f. Bakteriol., orig., 1913, 70, 115) — conditions which favor 
the formation of "spores" in certain acid-fast bacteria. 
- For chemical composition of fatty substance of the tubercle bacillus see deSchweinitz 
and Dorset: Jour. Am. Chem. Soc, 1898, 20, 618; 20th Annual Report, Bur. Animal 
Indus., 1903. Levene: Med. Rec, 1898, 54, 873; Jour. Med. Res., 1901, 6, 120; 
1904, 12, 251. Kresling: Centralbl. f. Bakteriol., orig., 1901, 30, 897. An excellent 
discussion of the chemistry of tuberculosis is by Wells, DeWitt and Long, 1923. 
3 Wolbach and Ernst: Jour. Med. Res., 1903, 10, 313. 
* Ziehl: Deutsch. med. Wchnschr., 1882, 8, 451. Neelsen: Fortschr. d. Med., 
1885, 3, 200. 
