358 PATHOGENIC MICROORGANISMS 



Hiss * devised a medium composed of beef serum one part, and dis- 

 tilled water two parts, to which is added one per cent of inulin (c. p.), 

 and enough litmus to render the medium a clear, transparent blue. 

 By fermentation of the inulin the pneumococcus acidifies this mixture, 

 rendering the litmus red and causing coagulation of the serum. Strep- 

 tococci do not ferment inulin ami the medium remains blue and fluid. 

 (For the preparation of special media, see section on Media, p. 132.) 



For the isolation of pneumococci from mixed cultures or from 

 material containing other species, such as sputum, the most reliable 

 method is to make surface smears of the material containing the bac- 

 teria upon plates of neutral glucose-agar or preferably of glucose-serum- 

 agar. According to the number of bacteria present in the infected ma- 

 terial from which the isolation is to be made, it may be smeared 

 directly upon the plate, or diluted with sterile broth or salt solution 

 before planting. After incubation for twenty-four hours, the pneumo- 

 coccus colonies are easily differentiated from all but those of strepto- 

 coccus. With practice, however, they may be distinguished froin these 

 also, by their smoother edges and greater transparency and flat- 

 ness. Pour-plates, prepared in the usual way, can also be made but 

 are less useful since deep colonies of pneumococci show no distinctive . 

 features. 



Another method for pneumococcus isolation, useful to eliminate 

 other bacteria, is that of animal inoculation. White mice are inoc- 

 ulated with 0.5 to 1 c.c. of the infectious material by subcutaneous 

 injection, made most easily at the base of the tail. If virulent pneumo- 

 cocci are present in the inoculated material, death from septicemia 

 usually occurs within twenty-four to forty-eight hours. Surface smears 

 should be made on glucose-agar plates with the heart's blood. By 

 this method pure cultures may usually be obtained directly from the 

 mouse blood. 



Resistance. — Kept upon artificial media, the viability of the pneu- 

 mococcus is not great. Cultures upon agar or bouillon should, to be 

 kept alive, be transplanted every third or fourth day, if the cultures are 

 kept at incubator temperatures. In all media in which rapid acid 

 formation takes place, such as glucose media, the death of cultures may 

 occur even more rapidly. In media containing albumin and of a proper 

 degree of alkalinity, preservation for one or even two weeks is possible. 

 The longer the particular race has been kept upon artificial media, the 



Hiss, Jour. Exp. Med., vi, 1905. 



