CYTO-DIAGNOSIS 295 



yet yields numerous cells on centrifugalization. It usually 

 clots spontaneously. 



The cells are almost all lymphocytes, with perhaps some red 

 blood-corpuscles (Plate IX., Fig. i). There may also be a 

 few large endothelial cells, flat plates with a well-marked 

 nucleus, and often one or more nucleoli ; their characters will 

 be described more fully subsequently. They are cells which 

 have been desquamated from the pleura, and play no part in 

 the pathological process. 



In cases examined at an early stage there may be a few 

 polynuclear cells up to 15 per cent. As the case progresses, 

 these become fewer and fewer, and after the first week only 

 isolated specimens can be seen. The diagnosis may be 

 clinched in some of these cases by the demonstration of the 

 tubercle bacillus. 



Secondary Tuberculous Pleurisy. In this case the lympho- 

 cytes are mixed with polynuclear leucocytes in approximately 

 equal proportions; this is a reason for thinking that there is 

 a septic element superadded to the tuberculous one. As the 

 case progresses, the septic 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 poly- 

 nnclears may gradually disappear, and the case becomes a 

 simple tuberculous one. 



In tuberculous pyopneumothorax the polynuclears greatly 

 predominate, 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 (/.?., 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 pro- 

 cess 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 



