THE PNEUMOCOCCUS AND PNEUMONIA 453 



definitely between some races of pneumococci and races of streptococci. 

 This difficulty is especially heightened when the piieumococcus has 

 become non-virulent, and at the same time no very typical morphology 

 or capsule formation is to be determined and a tendency to chain- 

 formation is marked. Cultures of pneumococci in such condition can- 

 not readily be distinguished morphologically from streptococcus cul- 

 tures. 



Under these circumstances recourse must be had to a careful bio- 

 logical study of the organism in question. The following are the 

 criteria mainly relied upon at present for the differentiation of these 

 two groups. 



Pneumococci ferment inulin, if cultivated in inulin-serum-water 

 medium. Acid formation from the inulin results within two days or 

 more in coagulation of the serum and reddening of the litmus. Strep- 

 tococci, because of their inability to attack the inulin, leave the 

 medium unchanged. 44 



Cultivated on whole-blood-agar, streptococci usually cause hemoly- 

 sis, pneumococci usually do not. 45 In contradistinction to Strepto- 

 coccus viridans which does not hemolyze, pneumococci have a tendency 

 on these media to form the black, dry, paint-blister colonies. 46 



Neufeld, 47 in 1900, noticed that normal rabbits' bile added in quan- 

 tities of 0.1 c.c. to each one or two cubic centimeters of a pneumococcus 

 broth culture caused lysis of the bacteria, rendering the culture fluid 

 transparent and clear. This does not occur with streptococci, and has 

 been used to differentiate the two species. According to Libman and 

 Rosenthal, 48 great reliance may be placed upon this method. 



The most convenient reagent for use in the Neufeld bile test is a 

 10 per cent solution of sodium taurochlorate in physiological salt solu- 

 tion. This should be sterilized or kept on ice. One-tenth volume of 

 such a solution produces prompt lysis in a broth culture of pneumo- 

 cocci. 



Decisive differential importance may be attached to the agglutina- 

 tions of these microorganisms in immune sera (see p. 462). 



The permanency of the various types in the pneumococcus-strepto- 



44 Hiss, Cent, f . Bakt., xxxi, 1902 ; Jour. Exp. Med., vi, 1905. 



45 Schottmuller, Miinch. med. Woch. 



46 Hiss, Jour. Exp. Med., vii, 1905. 



47 Neufeld, Zeit. f. Hyg., 1901. 



48 Libman and Bosenthal, Proc. N. Y. Path. Soe., March, 1908. 



