1. During the summer months 1928–9 an epizootic occurred in De Aar and neighbouring districts among small veld rodents, mainly affecting Namaqua gerbilles (Desmodillus auricularis).

2. Many of the animals dying showed a haemorrhagic septicaemia, the causative organism of which appeared to be a Pasteurella rather smaller in size than Pasteurella (Bacillus) pestis.

3. In a considerable proportion of the animals found dead there was no obvious septicaemia.

4. A description is given of the Pasteurella, which is believed to be a hitherto undescribed species, and for which the name Pasteurella desmodilli is suggested.

5. This organism was found to be highly pathogenic for rabbits, less so for guinea-pigs and mice, and non-pathogenic for rats and fowls.

6. It was found by Rhodes to be highly pathogenic for Lobengula gerbilles (Tatera lobengulae) from Cape Town, but for animals of this species from Johannesburg it proved to be much less virulent, and even when it killed them there was frequently no septicaemia.

7. The above observation seems to indicate the presence of a considerable degree of immunity among the Johannesburg lobengulas, as compared with those from Cape Town.

8. It is suggested that a similar condition of partial immunity among the Namaqua gerbilles (for which there is other evidence adduced) might account for the finding of many of them dead without obvious septicaemia.

9. The existence of this disease introduces a complication in the diagnosis of plague among veld rodents.