238 THE ACUTE PNEUMONIAS 



from the surface of agar or from bouillon, shorter or longer 

 chains may be observed (Fig. 66). After a few days' growth 

 they lose their regular shape and size, and involution forms 

 appear. Usually the pneumococcus does not grow below 22 C., 

 but forms in which the virulence has disappeared often grow 

 well at 20 C. Its optimum temperature is 37 C., its maximum 

 42 C. It is preferably an aerobe, but can exist without oxygen. 

 It prefers a slightly alkaline medium to a neutral, and does not 

 grow on an acid medium. In ordinary media, as just stated, 



the pneumococcus does 



t not usually appear to 



^ * develop a capsule, but 



ir* t *** **\\ according to Hiss, the 



f ,k ^ absence of a capsule is 



% *' / often only apparent, and 



f N** ^y* V if in making cover-glass 



( -\ ;t % preparations off such 



[ media some ox or rabbit 



\ /* \ ' serum be used as the 



\ % %< "\ y diluent, and the films 



\ - stained by his copper- 



** * ^ sulphate method (p. 



110), a capsule can be 

 demonstrated. Capsula- 

 ** tion frequently appears 



FIG. 66. Fraenkel's pneumococcus from a pure in fluid serum media, 



culture on blood agar of twenty-four hours' i rpaHilv rp 



growth, some in pairs, some in short chains. e> #'' c a J ^ 



Stained with weak carbol-fuchsin. x 1000. cognised if the organism 



be grown in rabbit or 



human serum which has been obtained under aseptic precautions 

 and heated for half an hour at 55 C. 



The pneumococcus ferments saccharose, ramnose, and lactose, 

 and a similar fermentative action on inulin is important, as 

 ordinary streptococci do not so readily ferment this sugar. 

 Apparently some samples of inulin are more readily acted on 

 than others. Usually the test is carried out with Hiss's inulin 

 serum water medium, in which coagulation of the serum results 

 (p. 47), but some investigators have had more success with 

 inulin bouillon, acid production being estimated by titration 

 against soda with a phenolphthalein indicator. 



There has been described by Eyre and Wash bourn a non- 

 pathogenic type of the pneumococcus which may be found in 

 the healthy mouth, and which may also be produced during the 

 saprophytic growth of the virulent form. From the latter it 



% / 



