282 PATHOGENIC BACTERIA. 



has all been replaced. Finally, the preparation is washed 

 in water containing i or 2 per cent, of sodium chlorid, 

 and may be examined at once in the salt solution, or 

 mounted in balsam after drying. The capsules are prob- 

 ably more distinct when the examination is made in 

 water. 



The pneumococcus is no stranger to us; it may some- 

 times be found in the saliva of healthy individuals, and 

 the inoculation of human saliva into rabbits frequently 

 causes a septicemia in which the bacillus is found abun- 

 dantly in the blood and tissues. Because of its frequent 

 presence in the saliva it was described by Fliigge as the 

 Bacillus septicus sputigenus. 



When desired for purposes of study, it may be obtained 

 by inoculating rabbits with pneumonic sputum and re- 

 covering the organisms from their heart's blood, or it may 

 be secured from the rusty sputum of pneumonia by the 

 method employed by Kitasato for securing tubercle ba- 

 cilli from sputum. A single mouthful of fresh sputum 

 is secured, washed in several changes of sterile water to 

 free it from bacteria of the mouth and pharynx, carefully 

 separated, and a central portion transferred to an appro- 

 priate culture-medium. 



The organism grows upon all the culture-media except 

 potato, but only between the temperature-extremes of 

 24 and 42 C. ; the best development is at 37 C. The 

 growth is always limited, probably because the formic 

 acid produced serves to check it. The addition of an 

 unusual amount of alkali to the culture-medium favors 

 the growth. 



The organisms readily lose their virulence in culture- 

 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 

 ioo° C M and alkalinized 4 c.cm. of normal caustic soda 



