This form is abundantly present in the lesions of glanders, is readily cultivated, and easily communicated to animals.

The bacillus is a rod somewhat like the tubercle bacillus, but slightly thicker and shorter. It is generally slightly curved, and usually single or in pairs. It is not motile. It is not certain that it produces spores.

The bacillus may be stained with the ordinary aniline dyes, especially with fuchsine, but better results are obtained with Loeffler's methyl-blue. The organism is completely decolorized by Gram's method.

The bacilli have been cultivated on glycerine-agar and blood serum, where they give a whitish or yellow culture. On potato there is a very characteristic growth, at first amber coloured, then becoming darker till it assumes a reddish brown or red tint with a yellowish-green colour peripherally. A temperature between 25° and 42° C. is necessary, the best results being obtained between 30° and 40°.

Animals are readily inoculated, but there are peculiar differences in susceptibility. As the disease is mainly one of horses, it is natural to find that these animals and asses are readily affected. Field mice and guinea-pigs are readily affected, but white mice, house mice, pigs, and cattle are hardly affected. There is always a local action at the point of inoculation, from which there may be a gradual extension, but not by the blood.

In man an accidental infection sometimes occurs, resulting in local abscesses, with secondary extension to the mucous membranes, joints, etc.

A remarkable fact is, that in cultivating the bacillus, it gradually loses its infective power, so that in the fourth or fifth generation it has become so harmless that it is necessary to inoculate much larger quantities, and the effect is merely local. By further cultivation the bacilli lose their virulence.

Fig. 152. - Actinomycosis. Tongue of cow. Clusters of heads are seen.