506 LEPROSY AND ACID-FAST BACTERIA 
shorter and relatively thicker. Occasionally isolated organisms exhibit 
swollen, club-shaped ends and branchino; is frequently observed in 
cultures in artificial media. They stain with difficulty and resist the 
combined decolorizinii^ action of mineral acids and alcohol. 
Isolation and Culture.— The organisms grow readily and rapidly on 
ordinary media, and after three or four days' incubation, the colonies 
are round, somewhat waxy in appearance, and vary in diameter from 
2 to 5 mm. Typical colonies are yellowish to a dark orange in color. 
Subcultures are obtained very readily. 
Pathogenesis. — Bacillus phlei is not pathogenic for man, so far as is 
known, but the introduction of large numbers of the organisms into 
the peritoneal cavity of guinea-pigs leads to the formation of localized 
nodules which eventually soften and contain a purulent, somewhat 
caseous mass. Typical tubercles with giant-cell and epithelioid-cell 
formation are not observed. Moderate doses do not cause death, but 
very large doses frequently lead to fatal results. The inoculated 
animals fail to give any reaction whatsoever with tuberculin derived 
from human or bovine cultures. 
The organisms are of practical importance because they may be 
confused with the tubercle bacillus. A simple microscopic examina- 
tion may in rare instances lead to error, but the correct differentiation 
between these organisms and the tubercle bacillus may be safely 
arrived at by their injection into guinea-pigs and the subsequent 
negatiA'c reaction with a fairly large dose of tuberculin. 
The Butter Bacillus.— This organism was first described by Rabino- 
vitsch,^ and subsequently her observations were confirmed and extended 
by Petri.2 
Morphologically the organisms are very similar to tubercle bacilli, 
but they are relativel}' less acid-fast. Dift'erentiation between the 
butter bacillus and the tubercle bacillus, however, cannot be made 
upon this basis. The organisms grow in culture media very like the 
grass bacilli. In broth the medium remains clear and the organisms 
form a thick, wrinkled pellicle on the surface. Very frequently there 
is a distinct ammoniacal odor to the broth, and it is said that they 
form small amounts of indol. 
So far as is known the butter bacilli are non-pathogenic for man 
and the lesions they induce in guinea-pigs are very similar to those 
produced by the grass bacilli. They are chiefly confusing when they 
are found in milk and butter because of their resemblance to the bovine 
tubercle bacillus. A distinction between the butter bacillus and the 
bovine tubercle bacillus can be definitely made by injection into guinea- 
pigs. The lesions are not tubercular in nature, and the animals fail 
to react to tuberculin. 
1 Ztschr. f. Hyg., 1897, 26, 90. 
2 Hyg. Rund., August 15, 1897. 
