CYTO-DIAGNOSIS 235 



or two, wash, stain in carbol thionin for two minutes, wash, dry 

 and mount. This renders everything very distinct except (some- 

 times) the nucleoli of the endothelial cells and the granules of the 

 polynuclears. Where the latter have to be inquired into (which 

 rarely happens) the film must be fixed with heat and stained with 

 triacid (p. 204). 



Cells met with in Exudates. 



Leucocytes derived from the blood are present in the majority 

 of exudates, and in most cases they are of ordinary appearance, 

 and readily recognised from the descriptions already given. The 

 polynuclears, however, may undergo various forms of degeneration, 

 and become so altered that their nature may be difficult to make 

 out. This occurs mainly in old exudates, especially in pus. 

 There are three chief forms : 



(a) In some cases the nucleus undergoes fragmentation — i.e., 

 breaks up into several isolated masses, so that the cell becomes 

 truly polynuclear (Plate IX., Fig. 2, where the ingested leuco- 

 cytes are fragmented). These masses stain deeply, and the cell 

 is easy to recognise, but it often happens that the fragments 

 of the nuclei are set free, and may then be mistaken for small 

 lymphocytes. If a specimen be stained by the triacid stain, they 

 may often be distinguished by a few granules which remain 

 adherent to the nucleus. 



(6) Dropsy oi the nucleus, which converts it into a large circular 

 or reniform mass which stains faintly. In this case the cell 

 resembles a large lymphocyte, large hyaline leucocyte, or myelo- 

 cyte. It may usually be distinguished from the former by the 

 presence of granulations, and the latter is not known to occur 

 in exudates except in cases of leucocythaemia. 



(c) Fatty degeneration of the cell, shown by the occurrence of 

 clear refractile granules with sharp 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 

 sUghtest 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. 



