1. Bacillus malleiand its poison produce a variety of vascular lesions in the rabbit and the guinea pig. 2. The type of the lesion depends upon, (a) the virulence of the culture, (b) the sex of the animal and (c) the degree of acquired immunity. 3. The vascular changes of a proliferative and degenerative nature produced by the slow action of the glanders poison in rabbits and guinea pigs are analogous to the vascular lesions caused by sub-acute glanders infection in man. 4. The most common site of the glanders vascular lesions of animals and man is the peripheral vessels, and especially the smaller visceral arteries. 5. The aorta is a less common site of the experimental lesions. 6. The vascular lesions produced experimentally by Bacillus mallei and its poison consist of three processes, (a) exudation, (b) proliferation, (c) degeneration. 7. The lesions produced by sub-acute glanders in man consist of two processes, proliferation and degeneration. 8. The primary reaction of the vessels in experimental animals and in sub-acute human glanders consists of a proliferation of the endothelium of the intima. 9. The first degenerative changes observed in experimental animals and in sub-acute human glanders occur in the "innermost layer" of the media and not in the so-called " middle zone." 10. The cause of the degenerative change in the inner layer of the media appears to be interference with the nourishment of the circular muscle fibres of the media by proliferation of the endothelium of the intima.