DIPLOCOCCUS PNEUMONIA 357 



slowly and sparsely as minute, grayish-white, transparent colonies. 

 The gelatin is not liquefied by the organisms. 



Growth upon milk is rapid and profuse, resulting usually in the 

 production of aoicl and consequent coagulation of the medium. Ex- 

 ceptionally, races are encountered in which this function is suppressed 

 and coagulation in milk is absent or long delayed. 



Upon potato, a thin, grayish, moist growth occurs, hardly visible to 

 the naked eye, and often indistinguishable from an increased moisture 

 on the surface of the medium. 



Upon Loeffler's coagulated blood serum, the pneumococcus develops 

 into moist, watery, discrete colonies which tend to disappear by a 

 drying out of the colonies after some days, differing in this from strep- 

 tococcus colonies, which, though also discrete, are usually more opaque 

 and whiter in appearance than those of the pneumococcus and remain 

 unchanged for a longer time. This medium, as will be seen, is use- 

 ful in differentiating pneumococci from the so-called Streptococcus 

 mucosus. 



Upon a medium made up of mixtures of whole rabbit's blood and 

 agar, the pneumococcus grows with considerable luxuriance, and forms, 

 after four or five days or longer, thick black surface colonies, not unlike 

 small sun blisters on red paint. These colonies are easily distinguished 

 from the hemolyzing colonies of most streptococci, and are in this 

 respect of considerable differential value. ^ 



Special media of various descriptions have been devised for pneu- 

 mococcus cultivation. Thus, Guarnieri ^ has recommended a medium 

 with a pepton-beef-infusion basis rendered semisolid by mixtures of 

 agar and high percentages of gelatin. A modification of this medium 

 has been described by Welch ^ and has been much employed in work 

 with the pneumococcus. Cultivation within eggs and upon egg media" 

 has been advised and used by various observers. Wadsworth ^ has 

 recommended a medium composed of ascitic fluid to which three-tenths 

 per cent agar has been added — sufficient to give a soft jelly-like con- 

 sistency to the medium. He observed prolonged viability and the 

 preservation of the virulence in this medium. 



For the purpose of differentiating pneumococci from streptococci, 



^ Hiss, loc. eit. 



2 Guarnieri, Att. dell' Acad, di Roma, 1883. 



3 Welch, Johns Hopk. Hosp. BuU., iii, 1892. 

 * Sclavo, Riv. d'Igiene, 1894. 



» Wadsworth, Proc. N. Y. Path. Soc, 1903. 



