136 APPLIED BACTERIOLOGY 



have been aptly described by various authors as resembling 

 chains of pearls. A variety, first obtained by Behring, 

 which is sporeless for many generations, is produced by 

 heating the culture above blood-heat for some time, or by 

 cultivating several times on nutrient gelatine containing 

 01 per cent, of phenol. 



In speaking of the organism as it occurs in blood, it was 

 stated that the ends were slightly convex ; on cultivating 

 they become slightly concave, but neither of these modifica- 

 tions is ever so great as to interfere with the characteristic 

 squareness of appearance. This concavity is regarded as 

 indicating an attenuated virulence. Involution forms are 

 often seen in old and attenuated cultures. 



Growth on Media. — On the gelatine plate small spherical 

 colonies develop in the depth, which consist of closely- 

 twisted bands of bacilli chains. When the growth reaches 

 the surface, chains of bacilli at once begin to spread out 

 over the surface in the most beautiful wavy convolutions, 

 liquefying the gelatine. This stage is usually reached in 

 two days, and is most characteristic. In the gelatine stab, 

 growth takes place along the needle track, fine branching 

 filaments often growing out into the gelatine. Liquefaction 

 commences at the top of the stab, proceeding downwards in 

 a horizontal plane, upon which a mass of bacilli rest, leaving 

 the gelatine above clear and liquid. No pellicle is formed 

 on broth cultures. On agar-agar a thin, gray-white growth 

 takes place, and on potato a considerable white growth, both 

 usually containing a large number of spores. Blood serum 

 is slowly liquefied. An alkaline reaction is generally favour- 

 able to the growth of this organism, but it will be noted 

 above that it grows well on potatoes, which are normally 

 acid. The bacilli stain well and easily with aniline dyes, 

 and are not decolourised by Gram's staining method. The 

 spores have great resisting powers to all reagents, and can 



