Oliver and Wherry,' in a brief note, originally described and named the nonspore-bearing, black pigment producing anaerobic microorganism Bacterium melaninogenicum. They cultured it from the throat and elsewhere on human blood agar slants made anaerobic by the pyrogallic acid method, on which characteristic dark brown or black colonies became visible within one to two weeks in primary cultures. They stated that subcultures yield a confluent, black, dry layer of growth. As the growth increases the hemoglobin throughout the agar slant disappears, until finally the medium appears like a slant of plain agar. The bacterium was described as a somewhat polymorphic, gramnegative, nonmotile rod, in size about 0.8, x 1.O, to 3.0. These authors apparently did not use plating methods for isolation and purification of their cultures and it seems probable from their description that they did not obtain strictly pure cultures. In the study of numerous cultures during several months I have found that this organism exhibits to a marked degree the habit of growing in very intimate mixture with other bacteria, and that strictly pure cultures are obtained with considerable difficulty. Growth of pure cultures is uncertain, slow, and usually meager. Hemolysis is slight, and the complete destruction of the hemoglobin throughout a slant or plate does not occur. But a very few contaminating organisms, so few that they are easily overlooked, suffice to accelerate the rate of development, and to increase the degree of hemolysis very markedly. It is probable, also, that the authors did not observe the pigmentproducing bacterium in its most typical form. In a large number of cultures studied by me the organism found constantly associated with pigmented colonies appeared most commonly as very tiny paired cells, which might be designated as either cocci or bacilli. Most typically they were seen as somewhat elongated diplococci, the pairs averaging 1.0 long and 0.4p, wide. Bacillus forms reaching a length of 3.0Qt to 4.0tE and