OCCURRENCE OF CAUSATIVE AGENTS. 147 



but this takes place only in cultures, and not in the body, 

 and it is incapable, therefore, of explaining the crisis. The 

 focus of disease in the lung, as well as the sputum, contains 

 living bacteria both during and long after the occurrence of 

 the crisis. Often these retain their virulence throughout the 

 entire period. Should the virulence be diminished during 

 the crisis, it is, however, soon again augmented, as experience 

 has shown. It is, therefore, not the cocci, but the human 

 organism that .undergoes some change in the crisis : it be- 

 comes insusceptible to the diplococcus-virus that is, im- 

 mune. 



Transmission of Pneumonia. Infection with pneumonia 

 takes place principally through the respiratory passages. 

 Only in some cases of secondary, complicating pneumonia 

 may the microorganisms gain entrance into the lungs 

 through the blood-stream. Direct transmission of pneu- 

 monia from one individual to another appears possible, and 

 a considerable number of house-epidemics of pneumonia 

 have been reported. In the majority of cases an attack of 

 pneumonia probably results from the inhalation of pneumo- 

 cocci with the air ; or, more frequently, pneumococci that 

 have long been present in the mouth, the pharynx, or the 

 nose, are permitted by some accidental occurrence to gain 

 entrance into the lungs and there to set up inflammation. 

 Naturally, in connection with the epidemic distribution of 

 pneumonia, the possibility can not be excluded that the 

 accidental influence has been operative in all cases in com- 

 mon, that the pneumococcus need not be transmitted from 

 one person to another, but that it was present previously in 

 all affected. 



The hereditary transmission of pneumonia from the 

 mother to the fetus is a matter of great interest. A few 

 cases have been reported in which the children of pneu- 

 monic mothers have been born with pneumonia. In gen- 

 eral the pneumococcus is not disseminated outside the 

 lungs of the infected individual. The slighter degree of 

 susceptibility of human beings protects them, as a rule, 

 against septicemic infection, which occurs regularly, for in- 

 stance, in the more susceptible rabbit. In some cases, 

 however, the pneumococcus has been found, also, in the 

 blood of pneumonic patients during life. Such cases have 

 always been marked by especial severity, with a fatal ter- 

 mination, so that the discovery of pneumococci in the cir- 



