THE STREPTOCOCCI 



405 



This may be obviated, especially when mass cultures are desired, 

 without sacrifice of the growth-increasing influence of the glucose, 

 by adding to the sugar-broth one per cent of sterile powdered CaCO. 9 



In milk, Streptococcus pyo genes grows readily with the forma- 

 tion of acid, followed, in most cases, by coagulation of the medium. 



On agar-plates at 37.5 C., grow.th appears within eighteen to 

 twenty-four hours. The colonies are small, grayish, and delicately 

 opalescent. They are round with smooth or very slightly corrugated 

 or lace-like edges, and rise from the surface of the medium in 

 regular arcs, like small droplets of fluid. Microscopically they 

 appear finely granular and occasionally, under high magnification, 

 may be seen to be composed of long in- 

 tertwining loops of streptococcus chains, 

 which form the lace-like edges. When 

 ascitic fluid or blood serum has been 

 added to agar, growth is more energetic 

 and the colonies correspondingly more 

 rapid in appearance and luxuriant in 

 development. In glucose-ascitic-agar, 

 acid formation from the sugar causes 

 coagulation of albumin with the conse- 

 quent formation of flaky white precipi- 

 tates throughout the medium. 10 



In gelatin stab-cultures growth takes 

 place slowly, appearing after twenty- 

 four to thirty-six hours as a very 

 thin white line, or as disconnected 



little spheres along the line of the stab. The colonies on 

 gelatin plates are similar in form to those on agar, but are usually 

 more opaque and more distinctly white. The gelatin is not liquefied 

 by the pyogenic streptococci, though certain of the more saprophytic 

 forms may occasionally bring about slow fluidification. 



On Loeffler's coagulated blood serum, growth is rapid and luxuriant 

 and may show a slight tendency to confluence if the medium is very 

 moist. Good chain formation takes place on this medium. 



Upon potatoes, growth is said not to take place. 11 



On media containing red blood cells, most pathogenic streptococci 



FIG. 47. STREPTOCOCCUS COL- 

 ONY ON SERUM AGAR. 



9 Hiss, Jour. Exp. Med., vi, 1905. 



10 Libman, Medical Record, Ivii, 1900. 



11 Frosch und Kolle, in Fliigge, ' ' Die Mikroorganismen, ' ' 1891. 



