THE PNEUMOCOCCUS 



285 



viability for nearly two weeks, but sunlight is rapidly fatal. The 

 virulence is rapidly lost during cultivation in artificial media, but it 

 may be retained practically unimpaired for weeks if the organisms 

 suspended in blood are sealed in glass tubes and maintained in the 

 dark at ice-box temperature. Pneumococci obtained from sputum, 

 either of healthy individuals or from the "rusty sputum" character- 

 istic of the earlier stages of lobar pneumonia, possess sufficient viru- 



FIG. 38. Pneumococcus in sputum. X 1000. 



lence to kill white mice. The original virulence may frequently be 

 restored to cultures on artificial media by passage through white 

 mice, provided large doses are administered at the start. Repeated, 

 rapid inoculations of virulent pneumococci frequently lead to a decided 

 increase of virulence above that originally exhibited by the organisms. 

 Products of Growth. Chemical. The pneumococcus produces acids, 

 chiefly lactic, but smaller amounts of formic acid, in hexoses, bioses, 

 and many starches. Hiss 1 has shown that the fermentation of inulin 

 by the pneumococcus is a very constant cultural differentiation of 

 the organism from the streptococcus, which is unable to ferment this 

 starch. Another important method of distinguishing between pneumo- 

 cocci and streptococci is the solubility of the former in bile or a freshly 

 prepared solution of sodium chlorate. 2 3 Colonies of the pneumococcus 

 on blood agar are surrounded by a greenish zone of methemoglobin. 4 



1 Jour. Exp. Med., August, 1905, vii., 547. 



2 Neufeld, Zeit. f. Hyg., 1900, xxxiv, 454. Wadsworth, Jour. Med. Research, 1904, 

 x, 228. 



3 The test is made as follows: 1 c.c. of a twenty-four-hour broth culture of the sus- 

 pected organism is mixed with 0.1 c.c. of a freshly-prepared 2 per cent, solution of sod- 

 ium chlorate and maintained at 37 C. Clearing of the solution indicating solution of 

 the organisms does not take place uniformly; some cultures dissolve more rapidly than 

 others. Cole, Jour. Exp. Med., 1912, xvi, 658. Acids interfere with the success of the 

 test. 



4 Butterfield and Peabody, loc. cit. Cole, loc. cit. 



