2Q4 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



Where inflammation takes place in a serous membrane the 

 first thing that happens is that the endothelial cells are set 

 free, so that they are always found with the leucocytes in the 

 early stages of pleurisy or peritonitis. If the inflammation is 

 severe they are destroyed, and the fluid at a later date does 

 not contain them, If the inflammation is less intense they 

 are stimulated to growth, and the young proliferating forms 

 are often very similar to the large lymphocytes and hyaline 

 leucocytes. They vary greatly in size, forming a continuous 

 series between a cell as larg'e as the large lymphocyte to one 

 as large as the plates described above. They are round or 

 oval, not mutually adapted, as in the endothelial cells which 

 have desquamated in passive exudates ; sometimes two hemi- 

 spherical cells may be found in apposition (Plate X., Fig. i). 

 The smaller (i.e., younger) the cells, 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 cer- 

 tainty from some types of endothelial cells at least, I must 

 confess myself unable to do so. Cells in mitosis are, of 

 course, very suggestive, but very rare, and there is no reason 

 w r hy they should not occur in ordinary active endothelium. 

 But malignant cells may occur grouped in a characteristic 

 way (see p. 296). 



PLEURITIC EFFUSIONS. 



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

 results most trustworthy. A diagnosis based on the subse- 

 quent rules will rarely be found erroneous. 



TUBERCULOUS PLEURISY. Two forms are to be recog- 

 nized : 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, 



