31S THE STREPTOCOCCUS-PNEUMOCOCCUS GROUP 
and Rosenow.^ The capsule is poorly formed or absent from pneii- 
mococci deri\'ed from chronic processes or from mucous surfaces 
where the organisms are growing as parasites or "opportunists." This 
may be significant in light of the observations of Neufeld- and of 
Stryker^ who showed that pneumococci cultivated in media containing 
homologous immune serum lost l^oth their virulence and the capacity 
to form capsules. 
The ordinary anilin dyes stain pneumococci readily, and they are 
Gram-positive when freshly isolated, but tend to become Gram- 
negative during cultivation in artificial media. 
Fig. 42. — Pneumococcus showing capsules. 
Isolation and Culture. — Pneumococci grow slowly and feebly upon 
ordinary laboratory- media, and they soon perish. Cultures may be 
obtained from the blood stream in a large percentage of cases from 
the fifth day of the disease to the crisis* by inoculating 5 to 10 cc. of 
blood into 100 to 150 cc. of 0.1 per cent glucose broth, and incubat- 
ing for twenty-four hours at 37° C. Isolation of pneumococci from 
sputum by cultural methods is usually very diflRcult ; but pure cultures 
may be obtained from the heart blood of white mice inoculated sub- 
cutaneously with sputum. 
The organisms may be obtained from inflammatory exudates and 
pus either by inoculaticm of the material into white mice or infecting 
the surface of blood agar, serum, ascitic or hydrocele agar plates. 
Colonies on blood agar plates are minute, gray and surrounded by a 
greenish halo which Butterfield and Peabody^ and Cole'' have shown 
to be methemoglobin. Colonies on ascitic agar are small, trans- 
parent and colorless. The growth upon plain nutrient agar or gelatin 
is very scanty. Gelatin is not liquefied. The addition of glucose to 
agar increases the nutritive value of the medium, but the acid formed 
1 Jour. Inf. Dis., 1911, 9, 1. 2 ztschr. f. Hyg., 1902, 40, 54. 
3 Jour. Exp. Med., 1916, 24, 49. * Rosenow: Jour. Inf. Dis., 1904, 1, 280. 
•^ Jour. Exp. Med., 191.3, 17, 587. « Ibid., 1914, 20, 363. 
