566 PATHOGENIC AEROBIC BACILLI 
Morphology.—Bacilli about as long as the typhoid bacillus, but not so 
thick, very frequently united in pairs ; occasionally grows out into filaments. 
Biological Characters.—An aérobic and facultative anaérobice, lique- 
fying, non-motile bacillus. Does not form spores. Thermal death point, 60° 
. Stains with the usual aniline colors but not by Gram’s method. Grows 
best at 10° to 15° C. The growth in gelatin is quite characteristic. At the 
end of two or three days, in gelatin plates, at the room temperature, small 
white colonies are developed ; in four or five days small gas bubbles or ex- 
cavations are seen, at the bottom of which lie the scale-like or rosetta-formed 
colonies. The margin of the colonies is irregular and later jagged. At 
first the colonies are grayish-white or yellowish, later brownish. The 
superficial colonies have a peculiar lustre. In gelatin stab cultures, colo- 
nies develop along the line of puncture, which at first resemble the growth 
of Streptococcus pyogenes, and no development is seen on the surface. At 
the end of five to seven days in place of the line of colonies is seen a channel 
filled with air, or gas developed by the separate colonies, the bubbles from 
which coalesce. The funnel formed in this way is somewhat larger above, 
and at the bottom contains a whitish sediment consisting of bacteria con- 
tained in a few drops of liquefied gelatin. Along the sides of the funnel 
bubble-like cavities may frequently be seen, at the bottom of which the bac- 
teria have accumulated. In bouillon a slight cloudiness is seen near the 
surface, on the walls of the test tube; when slightly shaken this falls to the 
bottom, leaving the bouillon entirely clear. In agar-agar tubes, a veil- 
like stripe develops along the line of puncture, and a grayish-yellow, moist 
layer, with irregular outlines upon the surface. After some weeks this 
acquires a brown color. No growth occurs upon potato. No development 
occurs in the incubating oven at 37° C. 
Pathogenesis.—Trout became infected and died through direct infection, 
subcutaneous or intramuscular inoculations, or through the addition of cul- 
tures to the water in which they were kept, or by placing infected fish in the 
same tank with healthy ones. 
BACILLUS OF BECK. 
Synonym.—Der Bacillus der Brustseuche beim Kaninchen. 
Obtained by Beck (1892) from rabbits which died of an infectious malady 
in the Institut fiir Infectionskrankheiten, in Berlin. 
Morphology.—Very small and slender bacilli, about twice as long and 
twice as thick as the influenza bacillus ; somewhat pointed at the extremities ; 
show a tendency to grow out into filaments. 
Biological Characters.—An aérobic (strict) non-liquefying, non-motile 
bacillus. Spore formation not observed. Grows at the room-temperature 
and more vigorously at 88° C. Does not stain by Grain’s method. Thermal 
death point, 50° C. (five minutes). Resists desiccation, at the room tempera- 
ture, for seventeen days, at 87° C. for three days. 
On gelatin plates, at tle end of forty-eight hours, small, finely granular, 
glass-like colonies are developed ; older colonies have a pale-brown appear- 
ance. In gelatin stab cultures a granular growth of a white color is seen 
along the line of puncture. Upon agar, at 37° C., an abundant development 
occurs in twenty-four hours. The line of puncture seen from above is gray- 
ish-white, by transmitted light bluish and porcelain-like with a brownish 
tint. On agar plates the colonies have a yellowish-gray appearance; the 
margin of the finely granular colonies is sharply defined. In agar cultures 
several days old the colonies are sticky and may be picked up as a compact 
mass, or drawn out into threads. In bouillon, at 37° C., there is a slight 
cloudiness at the end of twenty-four hours ; later the bouillon is clear and a 
white sediment is seen at the bottom of the tube. In bouillon cultures 
especially, the bacillus grows out into long filaments. 
