CYTO-DIAGNOSIS 293 



(r) Fatty degeneration of the cells, shown by the occurrence 

 of clear refractile granules with shar]3 contour. These are 

 only seen in wet preparations. In this case the cell usually 

 undergoes severe degenerative changes or even complete 

 solution, and in old pus it may be difficult to make out any 

 definite cells at all (Plate IX., Fig. 3). 



As a matter of fact, these degenerative changes rarely cause 

 the slightest difficulty in diagnosis. It frequently happens 

 that no pathologist is able to say definitely what is the nature 

 of any particular cell, but the nature of the cells as a whole is 

 usually obvious at a glance. 



Red corpuscles occur frequently, especially in tuberculous 

 and malignant exudates, which may be definitely haemor- 

 rhagic. It is necessary to distinguish corpuscles belonging to 

 the exudate, which are intimately mixed with it, from those 

 derived from the puncture, in which case the blood is most 

 marked at the beginning or end of the flow. 



Endothelial cells are very important, and it is necessary to 

 be able to recognize them at once. In certain passive 

 exudates (due to cardiac and renal disease) these cells occur 

 as large flat plates, exactly as if the endothelial coat had been 

 scraped off the pleura (Plate X., Fig. 2). They are then seen 

 to be much larger than the largest of leucocytes, and to have 

 a diameter three or four times that of a red corpuscle. Each 

 has a nucleus (sometimes more) which does not usually stain 

 very deeply, protoplasm which stains more faintly still, and 

 one or more nucleoli which stain very deeply in wet pre- 

 parations, less so in dry ones. 



These cells are often grouped into "placards" (Plate X., 

 Fig. 2), the edges of adjoining cells fitting into one another 

 like those of the counties on a map. The groups of cells 

 thus formed are always flat, and a careful focussing up and 

 down shows that they consist of a single layer of cells an 

 important fact, as it distinguishes them from masses of cells 

 of a malignant growth. 



Endothelial cells are very phagocytic, and ingest bacteria, 

 red corpuscles (Plate X., Fig. 3), leucocytes (Plate IX., Fig. 2), 

 etc. They often undergo fatty degeneration (Plate X., Fig. i) 

 or general degeneration, shown by their very faint staining; 

 complete solution of the protoplasm may occur, and the 

 nucleus be set free. It may then be mistaken for a 

 lymphocyte. 



