uber subsp. ietragenus. limy capsule. aa. Cells frequently united into groups of four 2a. Mxjcococcu 2. Colonies mucoid and spreading. a. Cells occur singly or in short chains; surrounded by a thick 3. Mycococcus capsulatus. aa. Cells occur in groups of four; surrounded by a thin, slimy capsule. 3a. Mycococcus capsulatus subsp. mucosus. B. Chromogenesis yellow. 1. Colonies bright yellow or brownish yellow. a. Colonies bright yellow; fermentative capacity weak. 4. Mycococcus luteus. aa. Colonies brownish yellow; fermentative capacity strong. 5. Mycococcus flavus. 2. Colonies yellow-green or lemon -yellow. 6 1. Mycococcus albus Krassilnikov, 1938. (Microbiologia (Russian), 7, Part I, 1938, 350.) al'bus. L. adj . albus white. Original description supplemented by material from Krassilnikov (Guide to the Actinomycetes, Izd. Akad. Nauk, U.S.S.R., Moskau, 1941, 124). Cells round or slightly ovoid, 0.7 to 1.0 micron in diameter. On some media, such as salt agar, are found rod-shaped cells, 0.7 by 1.0 to 1.2 microns, with wide branches. In 2- to 5-day-old cultures there are found large, spherical and lemon-shaped cells up to 1.5 microns in diameter; these frequently form on the surface of the medium when the culture has been seeded upon a fresh sub- strate. There are marked differences be- tween the daughter and mother cells. In old cultures many cells are changed into resting forms. Not acid-fast. Gram-positive. Gelatin: Rapid liquefaction. Colonies: Well developed on all media; large, moist and shiny. Malt agar: Excellent growth; colonies pasty. Synthetic agar with sucrose: Excellent growth. Glycerol agar: Excellent growth. Potato: Good growth by some strains. Milk: Coagulated and peptonized. Acetic acid and citric acid media: Good growth. Sucrose is inverted. Acid from glucose and fructose. Starch: Good growth; hydrolysis. No growth on paraffin. Comment: Krassilnikov (loc. cil.) recog- Mycococcus citreus. nizes two subspecies: Mycococcus albus subsp. albidus, distinctive because of its weak ability to attack substances, and Mycococcus albus subsp. lactis, distinctive because of the way in which it coagulates milk. Source: Isolated from soil at Yershovo Station, Russia. Habitat: Infrequently found in soil. la. Mycococcus albus subsp. albidus Kras- silnikov, 1941. (Guide to the Actinomycetes, Izd. Akad. Nauk, U.S.S.R., Moskau, 1941, 124.) al'bi.dus. L. adj. albidus white. Cells rounded or slightly angular, usually 0.6 to 0.7 micron in diameter, occurring singly or in short chains of 3 to 5 cells. Rod- shaped forms and enlarged forms have not been observed. Resting forms, 0.8 micron in diameter, are found in old cultures. Gelatin: Weak liquefaction. Colonies on solid nutrient media poorly developed; they are white and are smaller, flatter, smoother, more shiny and of a more compact consistency than those of Myco- coccus albus. Protein media: Good growth. Synthetic agar with sucrose: Good growth. Milk: Slow coagulation; weak peptoniza- tion; slightly alkaline. No acid from glucose, sucrose or lactose. Starch : Hydrolysis slow, forming a narrow zone of not more than 2 mm around the colony. Nitrites rapidly produced from nitrates. Proteolytic action weak. Comment: One culture (No. 25), after a
