action of Brown, Rockefeller Inst. Med. Res., Monograph 9, 1919, 8) on horse blood agar. Rare strains produce weak greening. No soluble hemolj'sin is produced. Both smooth and rough variants are ob- served as detected by colony forms and growth characteristics in broth. Rough variants often revert to smooth upon sub- culture in broth. Notwithstanding rather vigorous growth in culture media, cultures die out rapidl3^ Temperature relations: Optimum tem- perature, approximately 37° C. Growth at 45° C. but no growth at 10° C. No growth at 47° C. Does not survive 60° C. for 30 minutes. Tolerance tests : No growth in broth con- taining 6.5 per cent NaCl. No growth at pH 9.6, on 30 per cent bile blood agar or in milk containing 0.1 per cent methylene blue. Litmus milk: Acidified and curdled promptly by all lactose-fermenting strains. Litmus completel}' reduced after curdling. No digestion. Final pH in glucose broth, between 4.0 and 4.4. Produces large, mucoid colonies on agar medium containing 5 per cent sucrose or raffinose similar to those produced by Leuconosioc species. The polj^saccharides produced are a soluble, serologically active levan (not related to type specificity on other media) and an insoluble dextran. Colonies on sucrose agar may vary from "smooth" to "rough" depending upon the relative proportions of the two polysac- charides synthesized. These variations are not related to the smooth-rough variants observed in other media. Acid from glucose, maltose, sucrose, raf- finose, inulin and salicin. No acid from glycerol, mannitol, sorbitol, arabinose or xylose. Trehalose and lactose usually fer- mented. Some strains ferment only the ter- minal fructofuranose portion of the raffi- nose molecule, thus leaving melibiose as a metabolic product. Starch, sodium hippurate and gelatin not hydrolyzed. Esculin split. Ammonia is not produced from arginine. Distinctive character: Members of this species are most easilj' identified bj^ their characteristic colonies produced on agar media containing 5 per cent sucrose. Source: Saliva, sputum and intestinal tract of the human. Not pathogenic. Habitat: Human mouth, throat and naso- pharj'nx. 11. Streptococcus mitis Andrewes and Horder, 1906. (Lancet, 2, 1906, 712.) mi 'tis. L. adj. 7nitis mild. Description based on studies by Sherman, Niven and Smiley (Jour. Bact., 45, 1943, 249). Spherical or ellipsoidal cells 0.6 to 0.8 micron in diameter. Long axis of cell coin- cides with long axis of chain. Chain length may vary from moderately long to very long. Gram-positive. Serology: No group-specific antigen has been demonstrated. A very large number of serological types exists as determined by the precipitin and agglutinin reactions. Sero- logical typing is of little or no value in the identification of this species. Action on blood: Produces pronounced green zones (alpha hemolytic) of varying intensities on blood agar. No soluble hemol- ysin produced. Both smooth and rough variants are ob- served as detected by colony forms and growth characteristics in broth. Rough variants often revert to smooth upon sub- culture in broth. Cultures tend to die out rapidly in artificial media. Temperature relations: Optimum growth at approximately 37° C. Growth may or may not occur at 45° C. Does not survive 60° C. for 30 minutes. Tolerance tests: No growth in broth con- taining 6.5 per cent NaCl. No growth at pH 9.6, and only a minority of the strains grow on 10 per cent bile blood agar. No growth in litmus milk containing 0.01 per cent methylene blue. Litmus milk: Acidified and usually curdled promptly by the lactose-fermenting strains. Litmus reduced after curdling. No digestion. Final pH in glucose Inoth, between 4.2 and 5.8, usually about 4.5. Only rare strains produce large, mucoid colonies on 5 per cent sucrose agar. Some
