132 THE BLOOD 



according to their size, structure, and staining reaction. Some of these 

 cells are mononuclear, others polynuclear and many charged with special 

 types of granules that take now basic, now acid dyes, presumably accord- 

 ing to their clinical composition. The following varieties may be listed 

 for normal adult blood. 



1. Small mononuclear leucocytes, 22-25. 



2. Large mononuclear leucocytes, 1-2. 



3. Polynuclear neutrophilic leucocytes, 65-75. 



4. Polynuclear eosinophilic leucocytes, 1-4. 



5. Polynuclear basophilic leucocytes, mast cells, 0.2 to 0.5. 



The small mononuclear leucocytes, or lymphocytes, are about the size 

 of or smaller than the red corpuscles, a single nucleus with very little 

 nongranular protoplasm, staining deeply with methyline blue with a 

 lighter staining nucleus, 22 to 25 per cent. 



The large mononuclear leucocytes are double the size of the small leuco- 

 cytes or even larger. They have a single nucleus about the size of the 

 preceding type but a much larger relative development of protoplasm. 

 Their cytoplasm is not granular and they are weakly basophilic. These 

 cells like the small leucocytes arise in the lymphoid tissue. 



The polynuclear neutrophilic leucocytes are about the size of a red blood 

 corpuscle and are granular in appearance. The nuclei take basic dyes. 

 The cytoplasm is slightly acidic but the granules imbedded in it are baso- 

 philic. These leucocytes constitute from 65 to 75 per cent, of the total 

 number of white corpuscles. This class is most actively phagocytic and 

 is increased in number in response to most infections. 



The polynuclear eosinophilic leucocytes. The cells of this type are the 

 largest cells of the white corpuscle group. Their cytoplasm is crowded with 

 granules which stain deeply with eosin and other acid dyes. From this 

 characteristic they get their name. The eosinophiles constitute i to 4 

 per cent, of the total. They are extremely motile and phagocytic and are 

 very greatly increased in number in certain diseases. 



The mast cells are much fewer in number except in certain particular 

 diseases. They have a polymorphic nucleus characteristic in appearance. 

 They take basic dyes with difficulty. These cells are also granular. The 

 granules do not take eosin but are basic in type. They vary in size, being 

 rather larger than eosinophilic granules. In normal blood one mast cell 

 occurs in from 200 to 250 leucocytes. 



The relative number of leucocytes varies in children as compared with 

 normal adults. The small mononuclear lymphocytes are practically 

 double the adult number and the polymorphonuclears about half the 

 number in the adult. The eosinophiles are also more frequent though 

 still relatively rare. 



