230 THE ACUTE PNEUMONIAS 



settles to the bottom of the vessel as a slight dust-like deposit. 

 On potatoes, as a rule, no growth appears. Cultures may be 

 maintained for one or two months, if fresh sub-cultures are made 

 every four or five days, but they tend ultimately to die out. 

 They also rapidly lose their virulence, so that four or five days 

 after isolation from an animal's body their pathogenic action 

 is already diminished. Eyre and Washbourn, however, have 

 succeeded in maintaining cultures in a condition of constant 

 virulence for at least three months by growing the organisms 



on agar smeared with 



\ rabbit blood. The agar 



I * must be prepared with 



A' ** *s N Witte's peptone, must 



/ V v not be heated over 100 



^ ^ / C., and after neutralisa- 



| s -* ^* V tion (rosolic acid being 



i k t ;$y used as the indicator) 



must have '5 per cent, of 



^ ** \ normal sodium hydrate 



N V^ added. The tubes when 



\ v % inoculated are to be kept 



r *. \ at 37*5 C. and sealed 



i^ % to prevent evaporation. 



In ordinary artificial 



* ' media pneumococci usu- 



FIG. 66. Fraenkel's pueumococcus from a pure ally appear as diplococci 

 culture on blood agar of twenty-four hours' w : t i lont fl Par >milp but 

 growth, some in pairs, some in short chains. Wltnout a capsule, t 

 Stained with weak carbol-fuchsin. x 1000. in preparations made 



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 pneumo- 

 coccus 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 alka- 

 line medium to a neutral, and does not grow on an acid medium. 

 In ordinary media the pneumococcus does not usually appear to 

 develop a capsule, but according to Hiss, the absence of a capsule 

 is often only apparent, and if in making cover-glass preparations 

 off such media some ox or rabbit serum be used as the diluent, 

 and the films stained by his copper-sulphate method (p. 109), a 

 capsule can be demonstrated. Capsulation frequently appears 

 in fluid serum media, e.g., can be readily recognised if the 



