The occurrence of black colonies on anaerobic blood-agar cultures from carious teeth, etc., has been noted by several investigators. No one, so far as we are aware, has isolated and described the organism. We have isolated it from the throat, tonsils, infected surgical wound of the abdomen, from urine collected as aseptically as possible from a suspected focal infection of the kidney, and from the feces of a case of chronic dysentery superimposed on an original amebic infection. Isolation and Biologic Characters.?The bacterium grows readily at 37 C. on -f 1 human blood-agar slants made anaerobic by the pyrogallic acid method. In primary cultures, the colonies become visible within one to two weeks. Pure subcultures yield a confluent, black, dry layer of growth (fig. 1), within which lie the somewhat polymorphous rods, embedded in the masses of pigment. As the growth increases the hemoglobin throughout the agar slant disappears, until finally the medium appears like a slant of plain agar. The growth of the bacterium. on infusion agar is greatly facilitated by the presence of hemoglobin, and pigment production is absolutely dependent on it. In sodium phosphate broth (-f 1) the organism produces acid from dextrose, levulose, lactose, saccharose, maltose and mannite. Galactose is not attacked. On potato no growth occurs, nor does growth occur on agar or broth made from Liebig's beef extract, with or without dextrose or maltose. In gelatin containing pleuritic fluid there is a dense flocculent growth at 37 C, but no liquefaction. On Loeffler's blood serum a fairly luxuriant, white, moist layer of growth develops. Litmus milk is slowly acidified, but not coagulated. The bacterium occurs as somewhat polymorphous rods, in size about 0.8/aXI/a ? 3/x (fig. 2). They lose the stain in Gram's