320 THE STREPTOCOCCUS-PNEUMOCOCCUS GROUP 
has recently been found to be less reliable than was originally indi- 
cated. Another important method of distinguishing between pneu- 
mococci and streptococci is the solubility of the former in bile or a 
freshly prepared solution of sodium choleate.^'^ Falk and Young^ 
state that low concentrations of sodium choleate will also dissolve pneu- 
mococci. Colonies of the pneumococcus on blood agar are surrounded 
by a greenish zone of methemoglobin.^ 
Enzymes have not been demonstrated in cultures of the pneumo- 
coccus. 
ro.ri/z.?.— Soluble toxins have not been detected in cultures of pneu- 
mococci, although the filtrates obtained by Klemperer,^ Washbourn^ 
and Isaeff^ were toxic for small laboratory animals. The toxicity 
observed in these preparations was probably due to the liberation 
Fig. 4.3. — Pneumococcus in sputum. X 1000. 
of endotoxins as the result of autolysis of pneumococci in the medium 
or to the products of metabolism of the organisms. MacFadyen^ has 
obtained toxic substances from two- to three-day agar cultures of 
virulent pneun:iococci, which were ground finely after freezing with 
liquid air (method of MacFadyen and Roland), then extracted with 
1 to 1000 potassium hydrate, centrifugalized to remove fragments 
of the organisms and filtered. A small amount of the filtrate, 0.5 
1 Neufeld: Ztschr. f. Hyg., 1900, 34, 454. Wadsvvorth: Jour. Med. Res., 1904, 
10, 228. 
- The test is made as follows: 1 cc. of a twenty-four-hour broth culture of the sus- 
pected organism is mixed with 0.1 cc. of a freshly-prepared 2 per cent solution of sodium 
choleate and maintained at 37° C. Clearing of the solution, indicating solution of the 
organisms, does not take place uniformly; some cultures dissolve more rapidly than 
others (Cole: Jour. Exp. Med., 1912, 16, 658). Acids interfere with the success of 
the test. 
3 Jour. Infec. Dis., 1926, 38, 8. 
* Butterfield and Peabody: Loc. cit. Cole: Loc. cit. 
s Ztschr. klin. Med., 1892, 20, 165. 
6 Jour. Pathol, and BacterioL, 1896, 3, 214. 
" Ann. Inst. Pasteur, 189.3, 7, 260. 
s Centralbl. f. Bakteriol., orig., 1907, 43, .30. 
