CYTO-DIAGNOSIS 237 



(Plate X., Fig. i). The smaller (».«., younger) the cell, the smaller 

 IS the ring of protoplasm in proportion to the size of the nucleus, 

 and the more deeply does it stain. Cells of the type described 

 above will be referred to as " active " endothelial cells, in contra- 

 distinction to the " passive " plaques of desquamated endothelium. 

 Malignant Cells. — These cannot be distinguished with certainty 

 from some types of endothelial cells— at least, I must confess 

 myself unable to do so. Cells in mitosis are, of course, very sug- 

 gestive, but very rare, and there is no reason why they should not 

 occur in ordinary active endothelium. But malignant cells may 

 occur grouped in a characteristic way (p. 239). 



Pleuritic Effusions. 



It is in these that cyto-diagnosis is of chief value, and its results 

 most trustworthy. A diagnosis based on the subsequent rules 

 will rarely be found erroneous. 



Tuberculous Pleurisy. — Two forms are to be recognised : 

 the primary, the so-called idiopathic form, in which the prognosis 

 is good as regards immediate recovery, but which indicates a 

 great probability that the patient will subsequently become 

 phthisical ; and the secondary, which is due to the extension of a 

 tuberculous lesion to the surface of the lung, and is probably due 

 to tubercle plus mild sepsis. 



Primary Tuberculous Pleurisy. — The fluid is fairly clear, yet 

 yields numerous cells on centrifugalization. It usually clots 

 spontaneously. 



The cells are almost all lymphocytes, and there are 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 desqua- 

 mated from the pleura, and play no part in the pathological process. 



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

 nuclear 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 lymphocytes are 

 mixed with polynuclear leucocytes in approximately equal proportions ; 

 this is a reason for thinking that there is a septic element super- 

 added to the tuberculous one. As the case progresses, the septic 



