8TR. FMCALia 601 



diameter, and, on longer incubation, increase to a diameter of 1-2 mm. The colonies 

 are smooth, circular, low convex in elevation, with an entire edge ; they have a homo- 

 geneous, or shghtly granular structure, and show little differentiation. In streaked 

 cultures the colonies tend to be confluent, and growth may appear as a uniform film. 

 The growth is easily emulsified. 



In blood agar— some strains, corresponding to Lancefield's Group D hsemolytic strepto- 

 cocci, give )5-haemolysis. They form no filtrable hsemolysin when tested by the ordinary 

 methods, but a haemolysin of the oxygen-stable type may be demonstrated by special 

 cultiu-al methods. Most strams are non-hfemolytic. 



On MacConkey agar small pink colonies are formed. 



In broth there is an abundant, diffuse growth, with a very sUght deposit. No pellicle 

 formation occurs. 



On gelatin, there is a good growth, with colonies very similar to those produced on 

 agar. Gro^vth occurs at 10° C. Most strains fail to liquefy the gelatin, but a few do so. 



In gelatin stab, there is good growth, along the track, with little surface growth. Some 

 strains produce liquefaction, which is usually infundibuliform. 



Grows in medium containing 10 or 40 per cent, bile, La lactose agar of pH 9-6 or con- 

 taining 6-5 per cent. NaCl, in lactose broth containing 1 : 15,000 potassium tellurite, and 

 in milk containing 1 : 1,000 methylene blue. 



Heat Resistance and Viability. — Heat resistant. Withstands a temperature of 

 60° C. for 30 minutes. Survives in culture for a long time. Insoluble in bUe. Insensitive 

 to penicUlin. 



Biochemical Activities. — Usually fails to hydrolyse sodium hippm-ate. Produces 

 a final pH of 4-0-4-8 in glucose broth. Produces acid in lactose, mannitol, salicin, and 

 usually sucrose, trehalose and sorbitol, but not in raflfinose or inulin. Reduces the dye 

 and produces acid and clot in litmus mUk. Most strains reduce nitrates. Strains of the 

 liquefaciens and zymogenes varieties liquefy gelatia and digest casein. Some strains 

 produce HgS. 



Antigenic Structure. ^Possesses the Group D specific polysaccharide. There appear 

 to be several antigenic types. 



Pathogenicity and Toxin Production. — Most strains appear to be non-pathogenic, 

 or to possess a pathogenicity of a low order. They occasionally cause urinary infections 

 in man, or infections in relation to the intestinal tract. They have occasionally been 

 isolated from the blood stream, and are the cause of some cases of subacute endocarditis. 

 Most strains are non-pathogenic for laboratory animals. A few show some degree of 

 pathogenicity. There is no evidence that any of the streptococci forms a filtrable toxin. 

 Such strains as have been examined do not form a fibrinolysin acting on human fibrin. 



Differentiation within the Group. — There appear to be a number of varieties 

 of this organism, such as those called zymogenes, liquefaciens, and durans (see p. 585). 

 Whether these have any special habitat apart from the human intestine is not known. 



Str. lactis 

 This organism is foimd in milk and milk products, and on certain plants. Its differ- 

 entiation from Sir. fcecalis has been discussed in the body of the chapter (see p. 582). 

 Suffice it to say that the main distinguishing characters are as follows : it does not grow 

 at 45° C. ; it does not grow in lactose agar of pH 9-6 or containing 6-5 per cent. NaCl ; 

 it is killed by a temperature of 60° C. within 30 minutes ; it has no action on blood ; 

 mannitol, sucrose, and sorbitol are less readily fermented ; and the organism possesses 

 the Group N, not the Group D, specific polysaccharide. A cremoris variety has been 

 described. 



The characters of the other labelled groups or types of streptococci, as far as 

 we yet know them, have been sumraarized in the body of this chapter. 



