20 



These cells occur as isolated specimens in normal 

 blood. They form about o"5 per cent, of all white 

 cells. 



3. Platelets (Fig. 2). — Bodies of various 

 sizes up to one-third diameter of the red cell, . 

 nearly always lying in clumps of from six to fifty,: 

 and stained bright crimson. They often show a- 

 considerable amount of differential staining, but 

 differ entirely in appearance from parasites, more 

 especially in having no blue stained mass. An 

 isolated platelet lying upon a red cell may 

 simulate a parasite. For the difference between 

 it and a parasite, vide, above, platelets often: - 

 occur in large numbers in cases of malaria and, 

 perhaps, especially in blackwater fever. 



4. Blood Dust or Granules. — Small granules,- 

 smaller than micrococci. In fresh films they exhibit- 

 active motion (? Brownian). : 



^Hfr,o/j/(LSr 



Among abnormal constituents of blood we 

 may mention : — 



I . Nucleated Red Cells. — In conditions of loss or 

 destruction of blood cells, e.^.,, malaria, it is com- 

 mon to see nucleated forms of the red cell in the 

 blood. They are characterized by a small globular 

 nucleus with sometimes one or more little buds, 

 staining almost black with Romanowsky. If the 



