The disease in man is not so fatal as in cattle, for it remains local for a time at the site of infection, and this local disease can be successfully treated.
The beginning of our knowledge of the cause dates from 1851, when small rod-shaped bodies (Fig.

17) were found in the blood of the affected cattle, and by the work of a number of observers it was established that these bodies were constantly present.

Nothing was known of their nature; some held that they were living organisms, others that they were formed in the body as a result of the disease.
Next the causal relation of these bodies with the disease was shown and in several ways.

The disease could be caused in other cattle by injecting blood containing the rods beneath the skin, certainly no proof, for the blood might have contained in addition to the rods something which was the real cause of the disease.

Next it was shown that the blood of the unborn calf of a cow who died of the disease did not contain the rods, and the disease could not be produced by inoculating with the calf's blood although the blood of the mother was infectious.