CUL TIVA TION OF PNE UMOBA CILL US. 211 



they lose their regular shape and size, and involution forms 

 appear. Usually the pneumococcus does not grow below 

 22 G, but forms in which the virulence has disappeared 

 often grow well at 



20 C. Its optimum \ 



temperature is 37 JL^r- ^ As 



C, its maximum 42 \ S N 



C. It is preferably / \ 



an aerobe, but can % 



exist without oxy- s ** V g > 



gen. It prefers a \^, \ 



slightly alkaline \* ^ 



medium to a neutral, \ %jk 



and does not grow s % \ 



on an acid medium. ** * \ ^ 



These facts show that ^ ^ 



when growing out- 

 side the body on 



artificial media, the FIG. 58. Fraenkel's pneumococcus from a 

 rmfMimnrnrriic: ic a pure culture on blood agar of twenty-four hours' 



a growth, some in pairs, some in short chains. 



comparatively deli- Stained with weak carbol-fuchsin. x 1000. 

 cate organism. 



The Cultivation of Friedlander's Pneumobacillus. This 

 organism, when present in sputum or in a pneumonic lung, 

 can be readily separated by making ordinary gelatine plate 

 cultures, or a series of successive strokes on agar tubes. 

 The surface colonies always appear as white discs which 

 become raised from the surface so as to appear like little 

 knobs of ivory. From these, pure cultures can be readily 

 obtained. The appearance of a stab culture in gelatine 

 growth is very characteristic. At the site of the puncture, 

 there is on the surface a white growth heaped up, it may 

 be fully one - eighth of an inch above the level of the 

 gelatine ; along the needle track there is a white granular 

 appearance, so that the whole resembles a white round- 

 headed nail driven into the gelatine (Fig. 59). Hence the 

 name " nail-like " which has been applied. Occasionally 

 bubbles of gas develop along the line of growth. There is 



