338 PATHOGENIC ORGANISMS 



taken directly from the animal or human body, it is well to add to the 

 media animal albumin in the form of whole blood, blood serum, or asci- 

 tic or pleural transudates. Glucose, added in proportions of one to two 

 per cent, likewise renders media more favorable for streptococcus culti- 

 vation. Prolonged cultivation of all races upon artificial media renders 

 them less fastidious as to cultural requirements. The most favorable 

 reaction of media for streptococcus cultivation is moderate alkalinity 

 (two- tenths to five-tenths per cent alkalinity to phenolphthalein) . 

 Growth may be readily obtained, however, in neutral media or even in 

 these slightly acid. The optimum temperature for growth is at or about 

 37.5 C. Above 43 to 45 C., development ceases. At from 15 to 

 20 C., growth, while not energetic, still takes place, an important point 

 in the differentiation of these microorganisms from pneumococci. While 

 the free access of oxygen furnishes the most suitable environment 

 for most races of streptococci, complete anaerobiosis does not pre- 

 vent development in favorable media. Strictly anaerobic streptococci 

 have been cultivated from the human intestinal tract by Perrone * and 

 others. 



In alkaline bouillon at 37.5 C., pyogenic streptococci grow rapidly, 

 form long and tortuous chains, and have a tendency to form flakes which 

 rapidly sink to the bottom. Diffuse clouding occurs rarely and is a 

 characteristic rather of the shorter so-called Streptococcus brevis. 

 When sugar has been added to the broth the rapid formation of lactic 

 acid soon interferes with extensive development. 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 3 . 2 



In milk, Streptococcus pyogenes grows readily with the formation 

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



On agar-plates at 37.5 C., growth 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 intertwining 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 



1 Perrone, Ann. de 1'inst. Pasteur, xix, 1905. 

 , Jour. Exp. Med., vi, 1905. 



