Abstract
(1) One of three types of colony form can develop from a smooth colony of S. aboratus equi when a plate culture is maintained at room temperature for an additional 72 hours after the initial 24 hours incubation at 37°C. At present, except for their marked difference in colony form and their pathogenicity for mice, these three types could not be differentiated serologically. (2) The organisms which develop on an agar-agar medium after the inoculation of spleen, obtained from autopsied mice, which received cells of these three types, were inagglutinable by the H sera (e, n, x).
