THE PNEUMOCOCCUS AND PNEUMONIA 451 



tainty should exist and mistakes be made in identification is not sur- 

 prising when one considers the characters usually depended upon to 

 distinguish pneumococci from streptococci. Chief among these, as has 

 just been implied, are the morphological features which are, in the 

 case of pneumococci, a slightly lancet or elongated form rather than 

 the more typical coccus form characteristic of the streptococci, and an 

 arrangement of such cocci in pairs rather than in chains; added to 

 these features is the possession of a more or less well-defined capsule. 

 All of these characters are subject to variation or may be absent. Com- 

 pared with the morphological, the cultural characters are variable and 

 of minor importance. The pneumococcus colonies on coagulated blood 

 serum and on agar are moister and flatter, and the freshly isolated 

 pneumococcus is usually unable to develop readily or at all on gelatin 

 at below 22 C. 



The distinctness of the capsule of the pneumococcus in the body 

 fluids of man and animals and on blood serum, milk, or serum agar, 

 has been depended upon as the chief distinguishing and diagnostic 

 character. Nevertheless, instances have been reported of distinct cap- 

 sule formation by organisms which had either been previously identi- 

 fied as Streptococcus pyogenes, or at the time of the isolation could not 

 be definitely identified as belonging to this group or to the pneumo- 

 cocci, but were considered intermediate in character. 43 



43 Brief Description of Organisms Eeported as Capsulated Streptococci. Bordet 

 (Bordet, Ann. de 1'inst. Pasteur, 1897, xi, p. 177), working with an organism 

 previously identified as Streptococcus pyogenes, described such capsule formation 

 occurring in the peritoneal exudate of infected rabbits. 



Schuetz' (Schuetz, Cent. f. Bakt., Kef. 1, 1887, p. 393) Diplokokkus der 

 Brustseuche der Pferde, Poels and Nolen's (Poels und Nolen, Ford. d. Med., iv, 

 1886, p. 217) streptococcus of contagious pneumonia of cattle, and especially 

 the organism described by Bonome (Bonome, Ziegler's Beit., viii, 1890, p. 377) 

 as Streptococcus der meningitis cerebrospinalis epidemica, may all be looked upon 

 as organisms differentiated on insecure grounds from either pneumococcus or 

 streptococcus. The first two of these organisms, however, are said to be decolorized 

 by Gram's method, and as suggested by Frosch and Kolle (Frosch und Kolle, 

 Fliigge's ' ' Mikro-organis., ' ' ii, 1896, p. 161), in the case of Schuetz' organism 

 may belong to a group intermediate between Fraenkel's diplococcus and the 

 chicken-cholera group. 



Tavel and Krumbein (Tavel und Krumbein, Cent. f. Bakt., xviii, 1895, p. 547) 

 describe a streptococcus with a capsule, which was isolated from a small abscess 

 on the finger of a child. Capsules were also present in the artificial cultures, 

 and although ordinarily remaining uncolored, could be stained by Loeffler's 

 flagella stain. This organism was said to be differentiated from Fraenkel's 

 diplococcus and also in general from streptococcus (pyogenes) by a rapid and 



