458 



PATHOGENIC MICROORGANISMS 



PNEUMOCOCCUS INFECTIONS IN MAN, AND CLINICAL- 

 BACTERIOLOGICAL CONSIDERATIONS 



In man the most frequent lesion produced by the pneumococcus 

 is acute lobar pneumonia. About 90 per cent of all cases of this 

 disease are caused by the pneumococcus, the remainder being due 

 to streptococci, influenza bacilli, and other organisms, the relative 

 frequency of which, in this disease has been given in an earlier 

 section of this chapter. The relative frequency of the various pneu- 

 mococcus types in lobar pneumonia in and about New York is given 

 as follows by Avery, Chickering, Cole and Dochez, 65 from whose 

 work the following table is taken. 



TABLE 2 INCIDENCE OF TYPES OF PNEUMOCOCCUS IN LOBAR 



PNEUMONIA 



This table may be contrasted with the following, also the result 

 of work by the above named authors, which shows the distribution 

 of the different types in the mouths of normal individuals, a point 

 which has considerable importance in connection with the problem 

 of autoinfection with which we will deal in greater detail in speaking 

 of the epidemiology of the disease. 



There has been a great deal of discussion concerning the route 

 by which infection of the lung comes about after the pneumococcus 

 has entered a susceptible subject. The difficulties experienced by 

 many observers in infecting animals by direct instillation of pneu- 

 mococci into the lungs, have inclined many observers to assume that 



85 Avery, Checkering, Cole and Dochez, Monograph of the Eock. Inst., No. 7, 

 Oct. 16, 1917. 



