Bacteriologic Determination 339 



pneumonia patients varies in its power to agglutinate dif- 

 ferent pneumococci ; some strains were agglutinated, others 

 not. The sera of normal individuals and of normal rab- 

 bits possess no agglutinating power for pneumococci, the 

 atypical organisms, certain streptococci, and the Strepto- 

 coccus mucosus capsulatus. 



As pneumococci sometimes grow in chains instead of in 

 pairs, and as the capsules are not always more distinct than 

 the capsules that sometimes surround streptococci, it may 

 be necessary to resort to special methods of cultivation for 

 the final determination of the organism. One of the first 

 to be recommended is the use of the blood-agar plate, to 

 which reference has been made in the section upon Strepto- 

 coccus pyogenes. 



A second important method, and one that not only 

 differentiates the pneumococcus from the streptococcus, but 

 from the common organisms of similar morphology that 

 infect the mouth, is the inulin- serum-water fermentation 

 test of Hiss.* In using this medium, Ruediger f found it 

 best prepared as follows: Dissolve 5 grams of NaCl, 20 

 grams of Witte's peptone, and 20 grams of pure inulin in 

 looo c.c. of distilled water. Add 20 c.c. of a 5 per cent, solu- 

 tion of pure litmus and tube, putting 2 c.c. of the mixture 

 into each tube, and sterilize in the autoclave. After steril- 

 ization add (with a sterile pipette) 2 c.c. of sterile, heated 

 ascitic fluid, or, preferably, heated beef serum, to each tube, 

 and incubate twenty-four hours before using. Great care 

 must be taken not to use ascitic fluid that contains ferment- 

 able carbohydrates. Each lot must be tested with some 

 strongly fermentative bacterium, and the absence of ferment- 

 able carbohydrates proved. Ruediger prefers this prepa- 

 ration to the original solution of Hiss because he found that 

 some pneumococci would not grow on the latter. Fermenta- 

 tion of the inulin is regarded as characteristic of the pneumo- 

 coccus. 



The pneumococcus produces red colonies upon litmus 

 inulin-agar plates, which makes their use desirable when 

 pneumococci are to be isolated from saliva, throat secretions, 

 or other material in which similar appearing organisms 

 are apt to occur. Ruediger found no other mouth bacteria 

 that produced red colonies on these plates. 



* "Jour. Amer. Med. Assoc.," 1906, vol. XLVII, p. 1171. 

 t "Jour, of Exp. Med.," 1905, vol. vi, p. 317. 



