1. In the hog-cholera group the mutation from smooth (A) to granular (B) type occurs and a mutant with a moist, opaque colony formation was noted.
2. The B mutant when obtained pure remains a B type without reversion in the stock cultures.
3. The B mutant can be made to assume some of the A characters by rapid successive transplanting in bouillon.
4. The B mutant can usually be found in older transplants of A.
5. The two types may be distinguished by certain cultural characters, by slightly different agglutination reactions, and by different degrees of virulence.