t 



228 THE ACUTE PNEUMONIAS 



unstained halo, but is sometimes stained more deeply than the 

 ground of the preparation. This difference in staining depends, 

 in part at least, on the amount of decolorisation to which the 

 preparation has been subjected. The capsule is rather broader 

 than the body of the coccus, and has a sharply defined external 

 margin. The organism takes up the basic aniline stains with 

 great readiness and also retains the stain in Gram's method. 

 In any lesion many dead individuals often occur, and these 

 may be obviously degenerated and may lose their Gram-positive 



character. 



^" ■?>-. In sputum prepara- 



/■£ * ' ^ ja>- N tions the capsule of the 



pneumococcus may not 



W *■ m it A b e recognisable, and the 



^ * same is sometimes true of 



« *r ' * i lung preparations and of 



' I pneumococcal exudates in 



I other parts of the body. 



\i *# * ^ f Sometimes in prepara- 



\/» gSp; tions stained by ordinary 



* •> methods the difficulty of 



| * # . * . recognising the capsule 



« * ^ . when it - is present is 



^» due to the refractive 



index of the fluid in 



Fig. 58. — Fraenkel's pneumococcus in serous which the specimen is 



exudation at site of inoculation in a rabbit, mollr ,ted hpinir almost 



showing capsules stained. mountea oeing almost 



Stained by Rd. Muir's method, x 1000. identical with that of 



the capsule. This diffi- 

 culty can be overcome by having the groundwork of the pre- 

 paration tinted. 



The Cultivation of the Pneumococcus. — It is often difficult, 

 and sometimes impossible, to isolate this coccus directly from 

 pneumonic sputum. On culture media it has not a vigorous 

 growth, and when mixed with other bacteria it is apt to be 

 overgrown by the latter. To get a pure culture it is best to 

 insert a small piece of the sputum beneath the skin of a rabbit 

 or a »mouse. In about twenty-four to forty-eight hours the 

 animal will die, with numerous capsulated pneumococci through- 

 out its blood. From the heart-blood cultures can be easily 

 obtained. Cultures can also be got post mortem from the lungs 

 of pneumonic patients by streaking a number of agar or blood- 

 agar tubes with a scraping taken from the area of acute conges- 

 tion or commencing red hepatisation, and incubating them at 



