238 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



organisms may gain entrance in larger numbers, and the case 

 would become indistinguishable from an ordinary empyema unless 

 a cytological examination had been made early ; or, and this is 

 more usual, the polynuclears may gradually disappear, and the 

 case become a simple tuberculous one. 



In tuberculous pyopneumothorax the polynuclears greatly pre- 

 dominate, but lymphocytes are usually present in fair numbers. 

 The lesion is due to the bursting of a vomica or abscess that is 

 almost necessarily septic. 



" Septic " Exudates {i.e., those due to the pneumococcus, 

 streptococcus, gonococcus, and similar pyogenic bacteria). — The 

 characteristic cell is the polynuclear leucocyte. In the early 

 stages the films show these cells in large numbers, and they are 

 mixed with red corpuscles and with endothelial cells of active 

 type (Plate IX., Fig. 2). The pathogenic organism may be 

 distinguished either in films or in cultures. The process may 

 evolve on one of two lines, and in either case the cytology is 

 fairly characteristic. 



[a) The process is mild, and recovery takes place ; this is most 

 likely to occur when the inflammation is due to the gonococcus 

 (in joints especially) or to the pneumococcus in a strong subject. 

 The polynuclears and endothelial cells become more and more 

 scanty, and lymphocytes make their appearance in increasing 

 numbers. The discovery of these cells in a septic exudate is a 

 good sign ; the discovery of the pathogenic organism mainly or 

 entirely within the cells is another. 



(h) The process may pass on to suppuration. In this case the 

 endothelial cells become less and less abundant, and the poly- 

 nuclears become more numerous and undergo the various forms 

 of degeneration described above (Plate IX., Fig. 3). 



Cryptogenic Pleurisy, possibly due to True Rheumatism. 

 — In this case the predominating cell is the active endothelial cell 

 in various stages of fatty degeneration, and in addition there is a 

 comparatively small number of all the leucocytes in approxi- 

 mately the same proportions as in the blood, and a few red 

 corpuscles. The exudate is sterile. These appearances are 

 found in the very rare cases of true rheumatic pleurisy, and may 

 be regarded as a good sign, in that they do not indicate a tuber- 

 culous or septic origin (Plate X., Fig. i). 



Pleuritic Exudates due to Malignant Disease. — The 

 appearances vary, and a definite diagnosis cannot always be 



