DIPLOCOCCUS PNEUMONIA 357 



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

 The gelatin is not liquefied by the organisms. 



Growth upon milk is profuse, resulting in the production of acid and 

 coagulation of the medium. Races are encountered in which this is 

 suppressed and coagulation in milk is absent or long delayed. 



Upon potato, thin, gray, moist growth occurs, hardly visible and in- 

 distinguishable 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 streptococcus 

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

 whiter in appearance than those of the pneumococcus and remain un- 

 changed for a longer time. This medium, as will be seen, is useful in 

 differentiating pneumococci from the so-called Streptococcus mucosus. 



Upon mixtures of whole rabbit's blood and agar, the pneumococcus 

 grows well, and forms, after four or five days, thick black surface colo- 

 nies, not unlike sun blisters on red paint. These colonies are easily 

 distinguished from those of streptococci, and are of considerable differ- 

 ential value. 1 



Pneumococcus colonies on blood plates may cause a slight halo of 

 hemolysis and methemaglobin formation after 48 hours or longer in 

 the incubator. 



Guarnieri 2 has recommended a medium with a pepton-beef-infusion 

 basis rendered semisolid by mixtures of agar and gelatin. A modifica- 

 tion of this medium has been described by Welch 3 and has been much 

 employed. Cultivation within eggs and upon egg media 4 has been usedc 

 Wadsworth 5 has recommended a medium composed of ascitic fluid to 

 which agar has been added sufficient to give a soft jelly-like consist- 

 ency. He observed prolonged viability and the preservation of the 

 virulence on this medium. 



For the purpose of differentiating pneumococci from streptococci, 

 Hiss 6 devised a medium of beef serum one part, and distilled water two 

 parts, to which is added one per cent of inulin (c. p.), and enough litmus 

 to render the medium a clear, transparent blue. By fermentation of 

 the inulin the pneumococcus acidifies this mixture, causing coagulation 

 of the serum. Streptococci do not ferment inulin. 



1 Hiss, loc. cit. 3 Welch, Johns Hopk. Hosp. Bull v iii, 1892. 



2 Guarnieri, Att. dell' Acad. di Roma, 1883. 4 Sclavo, Riv. d'Igiene, 1894. 

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



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



