Pathogenic Bacteria

464 PA THOGENIC BA CTERIA.

able in length in artificial cultures than in the blood of
animals and of man. The bacilli occur singly, in pairs,
in clumps, and sometimes in short chains. When united,
an angle is often formed.

The bacillus is non-motile in both the ordinary hanging-
drops and in anaerobic culture. No mention is made of
the presence of flagella.

The organism stains well with the ordinary stains, and
retains the color well in Gram's method. When stained
with methylene blue a granular or vacuolated appearance

FlG. 132.—Bacillus aerogenes capsulatus (from photograph by Prof. Simon

Flexner).

is sometimes observable, due to the presence of unstained
dots in the protoplasm.

Usually in the body-fluids and often in cultures the ba-
cilli are surrounded by distinct capsules—clear, unstained
zones. To demonstrate this capsule to the best advan-
tage, Welch and Nuttall devised the following special
stain: a cover is thinly spread with the bacilli, dried, and
fixed without over-heating. Upon the surface prepared,
glacial acetic acid is dropped for a few moments, then al-
lowed to drain off, and at once replaced by a strong aque-
oiis solution of gentian violet, which is poured off and
renewed several times until the acid has been replaced by