OCCURRENCE OF CAUSATIVE AGENTS. 139 



tism, or general infection. The pleural effusions due to 

 general stasis (transudates attending heart-lesions, nephritis, 

 etc.) are, naturally, sterile, providing secondary infection 

 has not taken place, and for which the serous infiltration 

 of the tissues offers a favorable soil. 



The tubercle-bacillus and all of the pyogenic micro- 

 organisms are capable of inducing serous as well as puru- 

 lent pleurisy. 



The primary pleurisies (so-called pleurisies due to cold) 

 are most frequently dependent upon the tubercle-bacillus. 

 Next in frequency follows the diplococcus pneumoniae 

 Frankel, which plays a most important role, especially in 

 the pleural inflammations of childhood ; and, further, all 

 of the other pyogenic and phlogogenic microorganisms. 

 Whether in all of these cases the pleuritic effusion is really 

 primary can not always be determined with certainty, as 

 the smallest pulmonary lesions for instance, slight disease 

 of the apex or a bronchopneumonia that are scarcely sus- 

 ceptible of diagnosis clinically may induce pleuritis. 



The secondary pleurisies are associated in a portion of the 

 cases with the presence of the same bacteria that are 

 responsible for the primary disease. In the effusions that 

 so frequently occur in the sequence of pneumonia, in the 

 so-called metapneumonic exudates, there is encountered the 

 diplococcus ; in the effusions attending pulmonary tuber- 

 culosis, the tubercle-bacillus ; in the uncommon effusions 

 complicating typhoid fever, the bacillus of Gaff ky-Eberth ; 

 in the pleurisies that originate in purulent processes within 

 the abdominal cavity, the bacterium coli ; and so on. In 

 those diseases whose causative agents are as yet unknown 

 as, for instance, articular rheumatism and carcinoma 

 the accompanying pleural effusion has been examined for 

 bacteria, but as yet mostly with negative results. In an- 

 other portion of the cases these concomitant pleurisies are 

 dependent upon secondary or upon mixed infection. The 

 pleural effusion then contains the common exciting agents 

 of inflammation. Thus, in the empyema following scarlet 

 fever the streptococcus pyogenes is often found ; in that 

 following smallpox, staphylococci ; in that following influ- 

 enza, the diplococcus lanceolatus Frankel ; and so on. 

 Metastatic pleurisy, as part manifestation of a pyemic 

 general infection, is caused by the staphylococcus or the 

 streptococcus pyogenes. The same statement applies also 



