PATHOGENIC ANABROBIC BACILLI, 579 
Biological Characters.—An anaérobic, liquefying, motile 
bacillus. Forms spores. Grows at the room temperature, in the 
absence of oxygen, in the usual culture media. Grows best at a 
temperature of 36° to 38° C.; in nutrient gelatin, at 20° to 25° C., 
development is first seen at the end of three or four days ; does not 
grow at a temperature below 14° C. Spores are formed in cultures 
kept in the incubating oven at 36° C., at the end of thirty hours ; 
in gelatin cultures at 20° to 25° C., at the end of a week (Kitasato). 
The bacilli exhibit voluntary movements which are not very active ; 
those containing spores are not motile. It may be cultivated in an 
atmosphere of hydrogen, but does not grow in the presence of oxy- 
gen—strictly anaérobic—or in an atmosphere of carbon dioxide. 
The addition of one and one-half to two per cent of grape sugar to 
nutrient agar or gelatin causes the development to be more rapid 
Fie. 159. Fie. 160, 
Fie. 159.—Tetanus bacillus, from a gelatin culture. x 1,000. From a photomicrograph by 
Pfeiffer. 
Fria. 160.—Tetanusbacillus, from an agar culture ; spore-bearing rods. x 1,000. From a photo- 
micrograph by Pfeiffer. 
and abundant. The culture medium should have a feebly alkaline 
reaction. 
Colonies in gelatin plates, in an atmosphere of hydrogen, re- 
semble somewhat colonies of Bacillus subtilis, the opaque central 
portion being surrounded by a circle of diverging rays ; liquefaction 
is, however, much slower, and the resemblance is lost after a short 
time. Older colonies resemble the colonies of certain microscopic 
fungi, being made up of diverging rays. In long gelatin stab cul- 
tures development occurs along the line of puncture, at a consid- 
erable distance below the surface, in the form of a radiate out- 
growth ; the gelatin is slowly liquefied, and asmall amount of gas is 
at the same time formed. In peptonized bouillon having a slightly 
alkaline reaction, under hydrogen gas, the development is abundant 
