CHAPTER VII 

 PATHOGENICITY OF PNEUMOCOCCUS : MAN 



The infectiousness of pneumococci of the different serological 

 types for human beings; incidence and lethal powers of the cocci 

 in disease; their distribution in the body and the lesions pro- 

 duced; and the various phenomena of the carrier state. 



Pneumococci, if successful in passing the first defensive bar- 

 riers of the human system, may become localized in a tissue or 

 organ, mainly the lungs, whence they may invade the blood stream 

 and under favoring conditions incite metastatic foci in other parts 

 of the body ; or, after gaining entrance, they may proceed to sites 

 other than pulmonary tissue and there set up primary infection. 

 The nature and severity of the infection depend on the serological 

 type, virulence, and mass of invading cocci, the passage by which 

 they are admitted, and on the many and varied factors which con- 

 stitute natural resistance or which are involved in the creation of 

 specific immunity in response to the presence of the invading or- 

 ganisms. 



The epidemiology and the clinical and pathological aspects of 

 pneumococcal infection may be left to writers competent to discuss 

 these subjects.* Therefore, assuming that the reader of this review 

 is more intimately interested in the vital activities of Pneumococ- 

 cus as a microorganism than in the manifold morbid manifesta- 

 tions of the human body's response to its invasion, the present dis- 

 cussion is directed more particularly to the ability of pneumococci 

 of the different serological types to incite disease in man. 



Pneumococci frequently lead a vegetative existence in the nor- 

 mal mouth, abiding there without causing any appreciable disturb- 



* A contemporary review of the literature relating to these subjects has been 

 prepared by Heffron.soi 



