156 NORMAL AND PATHOLOGICAL BLOOD. 



Another characteristic is that it frequently appears as does the setting 

 in a ring. Some give the term microblast to smaller nucleated forms. 

 In normoblasts the red cell proper stains normally. The megaloblasts 

 not only have a greater diameter than the normoblast, but the nucleus 

 is poor in chromatin, stains less intensely and is less distinctly out- 

 lined. Instead of being round, the nucleus is irregular and may be 

 trefoil in shape. The cytoplasm surrounding the nucleus shows 

 polychromatophilia. This contrasted with the pure blue of the 

 lymphocytes should differentiate. Normoblasts are found in secondary 

 anaemias, and especially in myelogenous leukaemia. Megaloblasts 

 are peculiarly characteristic of pernicious anaemia. Enormous 

 megaloblasts are sometimes termed gigantoblasts. 



In aplastic anaemia (a severe type of pernicious anaemia), in con- 

 trast to ordinary pernicious anaemia, nucleated reds are very rarely 

 found. There is also very little poikilocytosis, and the color-index is 

 about normal. It is a rare, rapidly fatal anaemia, particularly of 

 young women. 



WHITE CELLS. 



Owing to the conflicting views as to origin, nature and functions of 

 the various leukocytes, their classification is in a state of confusion. 

 As regards the appearance of the cells, this of course varies as "the stain 

 used, and it requires considerable experience for a single individual to 

 be able to positively recognize the difference between a lymphocyte and 

 a large mononuclear when one specimen is stained with a Roman- 

 owsky stain, another with Ehrlich's triacid, and a third with haema- 

 toxylin and eosin. This, of course, is intensified when different persons 

 adhere to the method of staining which they prefer and are at a loss to 

 appreciate differences which are brought out by some other stain used by 

 some other person. Even with the same stain used with different speci- 

 mens of blood we find the staining characteristics of various leukocytes 

 imperceptibly merging, the one into the other, so that at times it is 

 impossible for one, even with his own standard of differentiation, to be 

 sure whether he is dealing with a lymphocyte or a large mononuclear. 

 The difficulty is even greater when w r e deal with Turck's irritation 

 forms and with myelocytes. 



