THE BLOOD TOO 



fading of the red cells, with the formation of prismatic crystals of 

 haemoglobin. 



The red blood cells number from 4,500,000 to 5,000,000 per cubic 

 millimeter of blood. 



2. White blood cells (leucocytes) (Fig. 53, 4 to 9 inclusive) are 

 colorless nucleated structures which have a generally si)herical shape, 

 but which are able to change their shape on account of their powers 

 of amoeboid movement. They have a diameter of from 5 to lo/i, 

 and are much less numerous than the red cells, the proportion being 

 about one white cell to live hundred red cells, or about 10,000 to the 

 cubic millimeter. This proportion is, however, subject to wide 

 variation. 



Leucocytes may be classified as follows: (a) Lymphocytes; (b) 

 mononuclear leucocytes; (c) transitional leucocytes; (d) polymor- 

 phonuclear or polynuclear leucocytes. 



(a) Lymphocytes (Fig. 53, 4). — These vary in diameter from 5 

 to 8/x, and are sometimes subdivided into small lymphocytes and 

 large lymphocytes. The nucleus is spherical, stains deeply, and al- 

 most completely fills the cell, the cytoplasm being confined to a 

 narrow zone around the nucleus. Lymphocytes constitute about 

 20-per-cent. of the white blood cells. 



(6) Mononuclear leucocytes (Fig. 53, 5 and 9) are of about 

 the same size as large lymphocytes. The nucleus, however, stains 

 more faintly and is smaller, while the cytoplasm is greater in amount. 

 From 2-per-cent. to 4-per-cent. of the white cells are mononuclear 

 leucocytes. 



(c) Transitional leucocytes (Fig. 53, 6) occur in about the 

 same numbers as the preceding, and are of about the same size. 

 There is relatively more cytoplasm, and the nucleus, instead of 

 being spherical, is crescentic or horseshoe or irregular in shape. 

 These cells represent a transitional stage between the mononuclear 

 and the polymorphonuclear and polynuclear varieties. 



(d) Polymorphonuclear and polynuclear leucocytes (Fig. 

 53, 7,8) constitute about 70-per-cent. of the white blood cells. Their 

 size is about the same as that of the mononuclear form, but they are 

 somewhat more irregular in shape. The appearance of the nucleus 

 is characteristic. In the polymorphonuclear form the nucleus con- 

 sists of several round, oval, or irregular nuclear masses connected 

 with one another by cords of nuclear substance. These cords are 

 frequently so delicate as to be distinguished with difficulty. The 



