Immune Serum 455 



agglutinate different pneumococci; some strains were aggluti- 

 nated, others not. The sera of normal individuals and of normal 

 rabbits possess no agglutinating power for pneumococci, the 

 atypical organisms, certain streptococci, or Streptococcus 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 identification of the or- 

 ganism. 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 

 Streptococcus 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, 

 Ruedigerf found it best prepared as follows: Dissolve 5 gm. of NaCl, 

 20 gm. of Witte's peptone, and 20 gm. of pure inulin in 1000 cc. of 

 distilled water. Add 20 cc. of a 5 per cent, solution of pure litmus, 

 and tube, putting 2 cc. of the mixture into each tube, and sterilize 

 in the autoclave. After sterilization add (with a sterile pipet) 2 

 cc. 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 fermentable 

 carbohydrates. Each lot must be tested with some strongly fer- 

 mentative bacterium, and the absence of fermentable carbohydrates 

 proved. Ruediger prefers this preparation to the original solution 

 of Hiss because he found that some pneumococci would not grow 

 on the latter. Fermentation of the inulin is regarded as character- 

 istic of the pneumococcus. 



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. 



Immunity. Pneumonia is peculiar in that the disease in human 

 beings terminates by crisis as though from some source a supply of 

 antitoxin or other immunizing agent was suddenly liberated, but 

 unfortunately also in that recovery is followed by immunity of such 

 brief duration as to permit the occurrence of frequent relapses. It 

 is also well known that many cases show a subsequent predisposition 

 to fresh attacks of the disease. 



Immune Serum. G. and F. KlempererJ have shown that the 

 serum of rabbits immunized against the pneumococcus protects 



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

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

 . J" Berliner klin. Wochenschrift,." 1891, Nos. 34 and 35. 



