496 Pneumonia 



"The medium was usually made from meat infusion and contained 

 1.5 to 2 per cent, peptone and 2.4 per cent. agar. Stock plates of 

 these media (serum-agar and 2 per cent, glucose-serum-agar) were 

 poured. The agar or glucose-agar was melted in large tubes and 

 allowed to cool down to a temperature below the coagulation point of 

 the serum. One-third volume of rich albuminous ascitic fluid was 

 added, and the resulting media poured into Petri plates. These were 

 tested by incubation and stored in the ice-chest ready for use. . . . 



"The plan finally adopted [for inoculating the plates] was as fol- 

 lows: A swab taken from the mouth was thoroughly shaken in a tube 

 of neutral bouillon. From this primary tube dilutions in bouillon 

 with four, six, and eight loops may be made. A small portion of the 

 dilute mixture was poured at a point near the periphery of the pre- 

 pared plates. By a slight tilting motion the fluid was carefully dis- 

 tributed over -the whole surface of the plates. Care must be taken 

 to avoid an excess of fluid. It was found that plates made in this 

 way gave a sufficiently thick and discrete distribution of surface col- 



Cultivation. The organism grows upon all the culture- 

 media except potato, but only between the temperature 

 extremes of 24 and 42 C., the best development being at 

 about 37 C. The growth is always meager, probably be- 

 cause of the metabolic formation of formic acid. The addi- 

 tion of alkali to the culture-medium favors the growth of 

 the pneumococcus by neutralizing this acid. Hiss and 

 Zinnser* advise that the culture-media used for the pneumo- 

 coccus be made with 3 to 4 per cent, of peptone. 



Colonies. The colonies which develop at 24 C. upon 

 gelatin plates (15 per cent, of gelatin should be used to 

 prevent melting at the temperature required) are described 

 as small, round, circumscribed, finely granular white points 

 which grow slowly, never attain any considerable size, 

 and do not liquefy the gelatin. 



If agar-agar be used instead of gelatin, and the plates 

 kept at the temperature of the body, the colonies appear 

 transparent, delicate, and dewdrop-like, scarcely visible to 

 the naked eye, but under the microscope appear distinctly 

 granular, a dark center being surrounded by a paler marginal 

 zone. 



Upon the medium recommended by Buerger for isolating 

 the pneumococcus, the colonies appear in from eighteen to 

 twenty-four hours, the surface colonies being circular and 

 disk-like. When viewed from above, the surface appears 

 glassy with a depressed center. When viewed from the side 

 or by transmitted light, they appear as distinct milky rings 

 with a transparent center. This " ring type " is regarded as 



* "Text-book of Bacteriology," 1910, p. 356. 



