CYTO-DIAGNOSIS 257 



endothelial cells which have desquamated in passive exudates; 

 sometimes two hemispherical cells may be found in apposition 

 (Plate X., Fig. i). The smaller {i.e., 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. 259). 



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 recognized : 

 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, 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 patho- 

 logical 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. 



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