PNEUMONIA. 337 



place of least resistance, are important factors. As a result, 

 the disease may be acute or chronic, wide-spread or local- 

 ized. Infection from the mouth or nose may lead to otitis 

 or to meningitis, especially in early life; whereas 



monia is more common in old age. 



ATTENUATION. Cultures from different sources show marked 

 difference in virulence. Cultures isolated from pneumonia in the 

 early stage are more virulent than those obtained later. When 

 grown on artificial media it rapidly attenuates and soon dies out, 

 unless it is passed through a susceptible animal, as a rabbit, every 

 few weeks. Attenuation in a few days at 42. The virulence and 

 vitality can be best preserved by drawing up the heart-blood of an 

 infected rabbit into sterile tube pipettes (Figs. 61 d, 62 a). These are 

 then sealed so as to leave as little oxygen as possible in the tube. 

 The blood-serum of rabbits is well adapted for growing the germ and 

 for maintaining its virulence. 



Diagnosis. The fact of the frequent presence of the 

 diplococcus in the normal saliva must be borne in mind 

 when examining the sputum of suspected pneumonia. 

 Moreover, it may happen that the diplococcus, which is 

 very abundant in the early stages of pneumonia, may be 

 rare or even absent from the later stages. The white 

 mouse, or the rabbit, may be given an intra-peritoneal in- 

 jection of the suspected material. Or, the latter may be 

 injected subcutaneously into the ear of a rabbit. In this 

 case ordinary sputum will not kill, whereas that of pneu- 

 monia will prove fatal in two or three days, or later. 



A microscopic examination of the sputum or exudates. 

 in man, or of the heart-blood of the animal should show 

 the typical capsulated, lance-shaped diplococcus, which 

 can be easily stained by Gram's method. Glycerin agar 

 plates should be developed at 20 and at 37. The Fraenkel 

 diplococcus will not grow, or only very exceptionally, at 20. 



Meningitis may be induced by other organisms than the pneu- 

 mococcus. Among these, especially deserving attention, is the Diplo- 

 coccus intracellularis meningitidis, which in many respects resembles the 

 gonococcus. The biscuit-shaped, flattened diplococci, which occur in 

 groups or within cells, do not stain by Gram's method. Unlike the 



gonococcus, they can be readily cultivated on agar at 37. 

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