1. From 1922 to 1926, mucoid types of Bact. lepisepticum have proved more prevalent that "D" types in certain rabbit communities.
2. The bacteria from the mucoid colonies are larger than the "D" type; "G" variants are very small. All types are largest during the period of logarithmic growth. Differences in size appear to be determined chiefly by the amount of "cytoplasmic" substance.
3. The mucoid colony is larger and appears watery as compared with the "D" colony.
4. Fermentation tests, indole and nitrate reduction reactions of mucoid and "D" types and their variants are similar.
5. The acid agglutination zone of the mucoid type is similar to that of the "D" type.
6. The mucoid type is more stable in suspension than the "D" type.
7. The negative potential of mucoid types is similar to that of the "D" and higher than that of "G" variants.
8. The behavior of the mucoid type of bacilli in fluid media differs from that of the "D" strains in the following respects. About 500 or more mucoid organisms per c., inoculated into plain broth, will grow; "D" strains require seedings of at least 100,000. A lag of 3 to 48 hours duration occurs in the growth of mucoid strains, according to the amount of original seeding. This is considerably longer than that observed for the "D" strains. The period of multiplication is relatively long—24 to 48 hours—and the maximum number per cc. does not exceed 600,000,000. "D" strains reach 1,000,000,000 per cc. within 24 hours. "G" variants appear very slowly in mucoid cultures as contrasted with "D" strains, where their occurrence is rapid and abundant. The presence in the broth of blood or other oxygen-absorbing substances enables less than ten mucoid organisms per cc. to multiply without lag and to reach a maximum number of about 600,000,000 per cc. in 24 to 48 hours. "D" strains reach a count of 1,000,000,000 per cc. within 12 hours under similar conditions.
9. "D" and mucoid strains, inoculated into 750 cc. of plain or blood broth, and incubated at 37°, remain alive for more than 12 months. The numbers per cc. decrease to about 1/1000 of the maximum after the first 6 weeks. Subsequently, the rate of decrease is slower. The original strains are gradually replaced by "intermediate" and "G" colonies.
10. The various mucoid strains proved similar in their antigenic properties. "D" strains were also mutually related, but no cross-agglutination between "D" and mucoid types was demonstrable.