Appendix I.
395
The bacillus has been described as both motile and non-motile, pos-
sibly this is true for young and old bacilli respectively. The bacilius
multiplies by fission ; a bacillus grows to a certain length and then
divides into two, and the process is repeated. Isolated spores which
have become free have never yet been seen.
In form and size Bacillus Lepræ greatly resembles Bacillus Tu-
berculosis. A distinction is considered to exist between these in
their behaviour to staining reagents, and this rests upon a micro-
chemical reaction dependent upon the behaviour of the investing
membrane of the bacillus towards acids, alkalies, and aniline dyes. 18
The staining procedure employed as diagnostic of the Bacillus Lepræ
is as follows : 1st, treatment of the section of tissue, or film fixed upon
a cover-glass, with warm Ziehl's solution 14 for twelve minutes ; 2nd,
decolorisation of the specimen in 25 per cent. nitric acid ; 3rd, wash-
ing in 60 per cent. alcohol ; 4th, washing in distilled water. Cover-
glass specimens are at once examined in water, or after drying, in
xylol-balsam. Sections are treated with absolute alcohol and removed
to bergamot oil before mounting in balsam. A saturated solution of
acetate of potash is the best medium in which to mount specimens,
as the colour disappears less rapidly. The Bacillus Tuberculosis is
not stained by so short an immersion in Ziehl's solution, and all
other bacilli that were stained would have been wholly decolorised
by the acid, while the Bacilli Lepras resist this bleaching 16 and stand
out in the field of the microscope as bright red rods (Baumgarten).
The following also stain well by the above method and exhibit a
resistance to strong mineral acids which is almost as great as that
shown by Tubercle and Leprosy Bacilli; (1) keratin tissue; (2) the
spores of a large kind of bacillus found in the intestinal canal and
described by Koch; (3) the spores of mucor; (4) certain pseudo-
bacilli figured by Celli and Guarnieri which are probably crystals of
fatty acid ; (5) the Syphilis, or Smegma Bacillus, which to some
( 13 ) Ehrlich's early papers are in Zeitschrift f. klin. Med. Bd. I, 1880; Ibidem Bd. II,
1881; Deutsch. Med. Wochen. 1882, No. 19; Charité Annalen 1SS6. The views of Ehrlich
with reference to the behaviour of Bacillus Lepras and Bacillus Tuberculosis towards aniline
dyes and also to acids, are, that, firstly, the membrane of these bacilli is only slightly permea-
ble to acids; and, secondly, that the acid chemically changes this membrane, so that the colour
held by the protoplasm cannot diffuse outwards. The value of the addition of alkalies, aniline
or phenol to the dye depends upon the facts that the membrane becomes more permeable, and
a true combination of these reagents with the dye ensures a more brilliant staining effect.
( 14 ) Water 100 cub. cent.; Crystallized Carbolic Acid 5 grammes; Alcohol 10 cub. cent.;
Fuchsin 1 gramme (Zichl-Neelsen).
( 15 ) As a fact, the bacilli do lose their colour wholly or in part in the acid, but regain it in
the treatment with alcohol and water. A piece of silk treated with aqeous methyl-violet simi-
larly reacts by losing colour in acid and recovering this in watter.