fore curdling milk, fails to ferment sorbitol, rarely ferments mannitol or sucrose and ferments glycerol only aerobically. Skad- hauge (Studies on Enterococci with Special Reference to Their Serological Properties, A Monograph, Copenhagen, 1950) reports that this species does not tolerate 1/2500 potassium tellurite in a medium, which is in contrast to the typical Streptococcus faecalis and its varieties. Source: Originally isolated from spray dried milk powder. Found in milk and dairy products and in the human intestine. Habitat: Intestines of humans and other warm-blooded animals. 18. Streptococcus lactis (Lister, 1873) Lohnis, 1909. (Bacterium lactis Lister, Quart. Jour. Micro. Sci., 13, 1873, 380; also see ibid., 18, 1878, 177; Lohnis, Cent. f. Bakt., II Abt., 22, 1909, 553.) lac'tis. L. noun lac milk; L. gen. noun lactis of milk. Ovoid cells elongated in direction of the chain; 0.5 to 1.0 micron in diameter. Occur mostly in pairs or short chains. Some cul- tures produce long chains. Gram-positive. Serologj': A group-specific antigen has been demonstrated (Sherman, Smiley and Niven, Jour. Dairy Sci., 23, 1940, 529; Seeleman and Nottbohm, Zent. f. Bakt., I Abt., Orig., 146, 1940, 142; Shattock and Mattick, Jour. Hyg., 43, 1943, 173). The serological group has been designated by Shattock and Mattick {loc. cit.) as group N. Manj' serological types are known to exist. Action on blood: Slight greening (alpha hemolytic) to indifferent (gamma hemo- lytic). Temperature relations : Growth at 10° but not at 45° C. May survive 60° C. for 30 minutes. Tolerance tests: Growth in broth con- taining 4 per cent NaCl but not in 6.5 per cent NaCl. Growth initiated at pH 9.2 but not at pH 9.6. Growth in milk containing 0.3 per cent methylene blue. Growth on 40 per cent bile blood agar. Litmus milk: Acidified, curdled, litmus completely reduced before curdling. Old laboratory strains may lose the ability to curdle milk. No digestion. Final pH in glucose broth, between 4.0 and 4.5. Acid from glucose, maltose and lactose. May or may not ferment xylose, arabinose, sucrose, trehalose, mannitol and salicin. No acid from raflinose, inulin, glycerol or sor- bitol. Strains have been isolated from plants that fail to ferment lactose (Yawger and Sherman, Jour. Dairy Sci., 20, 1937, 83). Orla-Jensen and Hansen (Zent. f. Bakt., II Abt., 86, 1932, 6) described certain strains that ferment raffinose. Starch and gelatin not hydrolyzed. So- dium hippurate and esculin may or may not be split. Ammonia produced from arginine. Ty- rosine not decarboxylated. This species is of great economic im- portance in the dairy industry. Certain strains are employed as starter cultures in preparing cheeses and cultured milk drinks. Some strains are capable of fermenting citric acid when incorporated with a fermentable sugar with the production of carbon dioxide, acetic acid and diacetjd. (See discussion and reference citations of citrate-ferment- ing strains by Swartling, Jour. Dairy Res., 18, 1951, 256.) For a recent discussion of the relationships of Streptococcus lactis to S. cretnoris and other lactic acid strepto- cocci, see Sherman (Jour. Dairy Sci., 38, 1955, 1184). Some cultures of this species synthesize a powerful antibiotic, nisin, that inhibits the growth of a wide variety of other Gram- positive microorganisms (Mattick and Hirsch, Nature, 154, 1944, 551; Hirsch, Jour. Gen. Microbiol., 5, 1951, 208). Distinctive characteristics: Growth at 10° or below and at 40° but not at 45° C; rapid and complete reduction of litmus before curdling milk; growth in the presence of 4 per cent but not in 6.5 per cent NaCl; am- monia produced from arginine; growth at pH 9.2 but not at pH 9.6; tyrosine not de- carboxylated. Source: A common contaminant in milk and dairy products. Habitat: Probably of plant origin (Stark and Sherman, Jour. Bact., SO, 1935, 639). 19. Slreplococcus crenioris Orla-
