192 



HUMAN PHYSIOLOGY 



III. Cells of Blood. 



1. Leucocytes White Cells. These are much less 

 numerous than the red cells, and their number varies 

 enormously in normal conditions. On an average there 

 are about 7500 per cubic millimetre. 



They are soft, extensile, elastic, and sticky, and each 

 contains a nucleus and a well-developed double centrosome. 

 In size they vary considerably, some being much larger than 

 the red cells, some slightly smaller. The character of the 



FIG. 100. Cells of the Blood, (a) Erythrocytes ; (b) Large, and (c) Small Lym- 

 phocyte ; (d) Polymorpho-uuclear Leucocyte ; (e) Eosinophil Leucocyte. 



nucleus varies greatly, and from this and variations in the 

 protoplasm, they may be divided into four classes. 



1st. Lymphocytes. Cells with a clear protoplasm and a 

 more or less circular nucleus. Some are very small, while 

 others are larger. They constitute about 20 to 25 per cent, 

 of the leucocytes (Fig. 100, b and c). 



2nd. Polymorpho-nuclear leucocytes, with a much distorted 

 and lobated irregular nucleus and a finely granular proto- 

 plasm, whose granules stain with acid and neutral stains. 

 These constitute about 70 to 75 per cent, of the leucocytes. 



3rd. Eosinophil or oxyphil leucocytes, with a lobated 

 nucleus like the last, but with large granules in the proto- 

 plasm which stain deeply with acid stains. From 1 to 4 

 per cent, of the leucocytes are of this variety. 



