614 



THE STREPTOCOCCI OF ANIMALS 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance. 



The infecting organism in this disease is a coccus about I/A in diameter, 

 round or somewhat oval and arranged in chains. In cultures the chains are 

 very long, often extending beyond the field of the microscope, while in milk 

 and in the affected tissues they are distinctly shorter. 



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FIG. 287. Streptococcus mammitis bo-vis. 

 Film from a broth culture. Carbol-thionin. 

 (Oc. II, obj. T Uh, Reich.) 



FIG. 288. Streptococcus mammitis bovis. 

 Film from the milk of an infected cow. 



Staining reactions. The streptococcus mammitis stains well with the basic 

 aniline dyes : it stains badly by Gram's method and is easily decolourized. 

 Films prepared with milk or cultures should be stained with carbol-thionin 

 or carbol-blue. 



Sections of the gland are best stained with carbol-blue and tannin (p. 217). 



2. Cultural characteristics. 



Conditions of growth. The streptococcus is indifferently aerobic ; the 

 ordinary media are quite suitable if slightly modified ; the optimum tem- 

 perature is from 35-37 C. and growth also takes place at room temperature. 



Characters of growth. Milk. The organism grows well in milk which it 

 turns acid and coagulates in about 34 hours. 



Broth. The most suitable broth is meat extract (p. 32) containing 2-4 

 per cent, of glucose or lactose. Incubated in this medium at 37 C. the 

 streptococcus rapidly forms a small whitish deposit sometimes flocculent 

 and consisting of long chains of cocci. When left undisturbed the medium 

 remains clear but becomes cloudy if gently shaken. 



The broth soon becomes very markedly acid and this stops further growth. 

 A richer culture and one which lives longer is obtained by adding 2 per 'cent. 

 calcium carbonate (p. 35) to the broth. Although the organism dies in a 

 few weeks in ordinary media it lives several months in media containing 

 calcium carbonate. 



Gelatin. Stab culture. After 3 or 4 days small, whitish, opaque, rounded 

 colonies appear, these then run together and form a thick line of growth. The 

 gelatin is never liquefied. 



Stroke culture. Small, rounded, translucent colonies are formed which 

 coalesce to form a pellicle thicker at the edges than in the centre. 



Agar. Serum. On these media the stroke cultures have the same charac- 

 teristics as on gelatin but the growth is more scanty. 



Potato. The organism either fails to grow altogether or produces a barely 

 visible film. 



