48 BIOLOGY OF PNEUMOCOCCUS 



Bieling, 114 by the use of laked blood agar, laked blood-optochin 

 agar, and boiled blood agar, could differentiate pneumococci, and 

 the longus and mitior types of streptococci. Presting 1109 used the 

 Bieling method in studying some sixty carefully identified strains 

 of pneumococci and streptococci, and concluded that boiled blood 

 agar was a suitable aid in differentiating pneumococci and green- 

 growing and hemolytic streptococci. On the laked blood agar the 

 hemolytic streptococci exhibited such marked variation that viri- 

 dans could not be distinguished from the hemolytic types, nor from 

 pneumococci. Koch, 731 after one year's favorable experience with 

 Bieling's blood-optochin agar, recommended the medium for the 

 differentiation of pneumococci and streptococci. 



The "polytrope" medium of Lange — a special lactose-mannite- 

 peptone bouillon — as reported by Haendel and Lange, 585 develops 

 a diffuse orange-yellow coloration when pneumococci of long arti- 

 ficial cultivation are grown on it, but remains uncolored when the 

 strains are cultivated directly from infected animal material. This 

 latter fact renders this medium unsuited to the differentiation of 

 bacterial species, because streptococcal strains of long cultivation, 

 and other bacterial species as well, cause no color change. Dog- 

 blood agar plates, according to Sia and Chung, 1270 give colony 

 differences sufficiently pronounced to enable one to distinguish 

 between colonies of smooth and rough strains of pneumococci. 

 For the same purpose, the authors, in a later communication, 1271 

 reported that a medium consisting of one per cent dextrose- 

 beef-infusion agar with a reaction equal to pH 7.8 containing 

 type-specific antipneumococcic serum served to identify the pneu- 

 mococcal type strain. In poured plates, the colonies under the sur- 

 face, when illuminated from the side on a dark background, showed 

 an annular opacity which was claimed to be type-specific. 



Thomson and Thomson, 1400 by means of photomicrographs of 

 colonies of pneumococci grown on plasma-testicular agar, claimed 

 that it was possible to detect significant species and even type dif- 

 ferences. Their excellent photographs repay study. 



