BIOLOGICAL PROPERTIES 585 



broth. In this medium the pneumococcus grows abundantly at 37 C. pro- 

 ducing a marked cloudiness of the medium and later a mucoid precipitate 

 very rich in micro-organisms. 



Liquid serum. The best serum is that prepared with young rabbit blood 

 collected aseptically and not heated : in such a serum a very copious growth 

 is obtained on incubating at 37 C. At first the medium is thickened and 

 becomes markedly turbid, and later a heavy precipitate composed of capsulated 

 pneumococci is thrown down. 



Milk. The pneumococcus coagulates milk [but not invariably, see p. 602]. 



Potato. No growth takes place on this medium. 



Inulin media. American observers recommend media containing inulin 

 for isolating and differentiating the pneumococcus. The pneumococcus does 

 not ferment inulin, herein presenting a contrast to the streptococci (cf. p. 602). 



Hiss uses the following medium : To 1 part of ox serum add 2 parts of distilled 

 water and 1 part per cent, of litmus solution. Heat to 100 C., add 1 per cent, of 

 inulin and sterilize on three successive days at a low temperature. 



Ruediger recommends the following medium for the isolation of the pneumo- 

 coccus : to 1 litre of broth add 15 grams of agar and 15 grams of inulin and, after 

 sterilization, 20 c.c. of a 5 per cent, solution of Merck's litmus. Distribute in tubes 

 and to each tube add 1 c.c. of ascitic fluid. 



SECTION III. BIOLOGICAL PROPERTIES. 

 1. Vitality and virulence. 



I. In sputum and in albuminous exudates the pneumococcus retains its 

 vitality and virulence for a long time and can resist even prolonged desicca- 

 tion (Bordoni) : it also shows prolonged vitality in the soil and in dust. Em- 

 merich found virulent pneumococci in the dust between the joists in wards 

 where pneumonia patients were lying, and Uffelmann discovered the organism 

 in the air of a vault. 



II. In artificial cultivation the pneumococcus soon loses its virulence and 

 even its vitality. Cultures on solidified serum and on agar die after 4 or 5 

 days ; cultures in liquid media remain alive longer, but are avirulent at the 

 end of a week. The less suited the medium is to the growth of the pneumo- 

 coccus the more rapidly does the virulence diminish ; thus it disappears more 

 quickly in ordinary broth than in blood-broth. According to Bezan9on and 

 Griffon, the pneumococcus will live for a year in defibrinated blood containing 

 ascitic fluid. (In this medium the pneumococcus appears as chains : sown 

 afterwards on agar or broth it preserves this inherited appearance but reverts 

 to the diplococcal form in rabbit-serum.) Defibrinated rabbit or dog blood 

 either pure (Gilbert and Fournier) or, better still, blood-agar (Bezangon and 

 Griffon) may also be used as media on which to preserve the vitality of the 

 organism. In ordinary media the virulence rapidly diminishes and is alto- 

 gether lost in the third sub-culture. 



Cultures are sterilized in 24 hours at a temperature of 42 C. ; in 10 minutes 

 at 56 C. and instantly at 65-70 C. Desiccation rapidly kills the organism 

 in culture. 



Pasteur showed that the attenuation in culture is largely due to the action of 

 the oxygen of the air ; hence it follows that the virulence can be maintained for a 

 long time in anaerobic culture (Frankel). In cultures on egg sown as described on 

 p. 53 (A) the organism will remain virulent for several months (Bunzl-Federn). An 

 efficient method of preserving the virulence of the pneumococcus is to inoculate the 

 culture into a rabbit, collect a little of the heart- blood post mortem, and store 

 it in a sealed pipette : in the pipette the blood retains its virulence for a very long 

 time. For future experiments sow the blood in broth, incubate for 24^36 hours 

 and inoculate the culture. 



