27 



Moreover, crescents again have quite definite out- 

 lines, and shew a red-stained central portion and 

 blue extremities. 



Fig. 3A. Pigmented Large Mononuclear Leucocytes 



The same criteria apply to the spherical form 

 of the crescent. 



4. Pigmented Leucocytes (Fig. 3A). — Large 

 leucocytes with a large nucleus. Pigment (melanin) 

 may occur scattered about the periphery of the 

 cell, or in little clumps, or even in very fine powdery 

 grains. The pigment is brownish-black in colour. 

 Skin pigment may be seen in epithelium scales or 

 free in the plasma, but the definite position of 

 the pigment in the protoplasm of the leucocyte 

 characterizes melanin. 



Appearances in a Fresh Specimen 



I. Rings. — The very small forms of these 

 are characteristic of malignant tertian infection. 

 They measure about one-seventh the diameter of 

 a red cell. A ' ring ' is characterized by its rather 

 opaque white look, its very definite contour, and 

 by the fact that the central portion is of the same 

 colour as the red cell, which is in fact seen through 

 its substance. The ring has often a thickening 

 at one point giving the 'signet ring' appear- 

 ance. On watching such a ring from time to time 



