198 BIOLOGY OF PNEUMOCOCCUS 



were divided into serological types. Eyre and Washbourn 378 in 

 1899 gave descriptions of four strains of pneumococci, of which 

 three, isolated from infections in man, were considered by the au- 

 thors to be parasites, and one strain, from the normal human 

 mouth, was looked upon as a saprophyte. The first three strains 

 displayed great capabilities both for acquiring and for retaining 

 a high degree of virulence, whereas the fourth culture possessed a 

 low capacity in both respects. 



The severity or lack of severity of an infection may depend on 

 a preceding or accompanying infection with another bacterial spe- 

 cies. For example, Sinigar (1903) 1292 described the ascending viru- 

 lence of a respiratory infection among the staff and patients in the 

 Leavesden Asylum. Beginning as a brief, indefinite illness, the dis- 

 ease gradually increased in severity, occasionally showing bron- 

 chial symptoms, and then developed into lobar pneumonia with a 

 high fatality-rate. In all the cases, it was alleged that pneumococci 

 were present in large numbers but, since there is no reference in 

 the text to cultivation or virulence tests, it is impossible to say 

 whether the same strain of Pneumococcus — if the organism was a 

 pneumococcus — gradually gaining virulence, was responsible for 

 the epidemic, or whether pneumococci of relatively low virulence 

 were succeeded by a type having greater infectivity. 



Kindborg (1905), 713 in a study of a large number of strains ob- 

 tained from normal and pneumonic sputum, empyema pus, and 

 other sources due to pneumococcal infection, observed wide limits 

 in the pathogenicity of the different cultures. The organisms from 

 cases of pneumonia were said usually to be the most virulent, while 

 strains isolated from local inflammatory processes were generally 

 avirulent. Whittle 1519 determined the virulence for mice of sixty 

 strains of pneumococci collected at random from infections in man, 

 and concluded from his tests that pneumococci by virtue of their 

 pathogenic powers could be divided into at least two groups ; those 

 of high virulence were responsible for such well-recognized clinical 



