348 PA THOGENIC BA CTERIA. 



media, and cease to be pathogenic after a few days. In his 

 experiments with antipneumococcic serum Washbourn 

 found, however, that a pneumococcus isolated from pneu- 

 monia sputum and passed through one mouse and nine 

 rabbits developed a permanent virulence when kept on 

 agar-agar made carefully, so that it was not heated beyond 

 100 C., and alkalinized 4 c.cm. of normal caustic soda 

 solution beyond the neutral point determined with rosalic 

 acid, to each liter. The agar-agar is first streaked with 

 sterile rabbit's blood, then inoculated. The cultures are 



FIG. 99. Diplococcus pneumoniae : colony twenty-four hours old upon gelatin ; 

 x 100 (Frankel and Pfeiffer). 



kept at 37.5 C. Not only is this true, but ordinarily 

 they seem to be unable to accommodate themselves to a 

 purely saprophytic life, and unless continually trans- 

 planted to new media die in a week or two, sometimes 

 sooner. 



Kinyoun recommended to the writer that virulence 

 could be retained for a considerable time by keeping 

 blood from an infected rabbit, in a hermetically sealed 

 glass tube, on ice. This plan seems to work admirably 

 if the blood is not kept too long. 



