226 CLINICAL BACTERIOLOGY AND H.EMATOLOGY 



DIFFERENTIAL LEUCOCYTE COUNT 



The following varieties of leucocytes are to be recognized, the 

 description in each case being taken from a preparation stained by 

 Jenner's method. 



A. Cells devoid of Granules. 



I. Lymphocytes (Plate VII., Figs, i, 2, 3, 4) are variable in size, 

 some being about as big as a red corpuscle, others nearly twice this 

 size. Each has a single nucleus, which is circular or nearly so, 

 and which stains a deep blue. The protoplasm forms a narrow 

 band round the nucleus, and also stains blue, often more deeply 

 than the nucleus. 



Variations of these cells occur. In some cases the whole seems 

 to stain uniformly, in which case it is probably a free nucleus 

 (Plate VII., Fig. 3). In others the protoplasm appears to be 

 studded with blue granules, which often lead beginners astray. 

 They are not true granules, but knots in the protoplasmic 

 network. 



In healthy adults they average about 25 per cent, of all the 

 leucocytes present, varying between 22 and 28 per cent. In 

 childhood they- are more numerous — up to 60 per cent. 



The small forms are the more numerous, but as no trustworthy 

 diagnostic information can be drawn from the proportions of the 

 large and small forms, they are usually counted together. Very 

 large forms are often abundant in acute lymphatic leucocythasmia. 



Large Hyaline or Large Mononuclear Leucocytes (Plate VII., 

 Figs. 5, 6). — These are the largest cells met with in normal 

 blood, and may have a diameter two and a half that of a red 

 corpuscle. They have a round, oval, kidney- shaped, or twisted 

 nucleus, which stains less deeply than those of the lymphocytes, 

 and has often a purplish colour. The protoplasm is relatively 

 more abundant than in the lymphocytes, and stains very faintly 

 of a bluish or purplish colour. It often has false granules similar 

 to those of lymphocytes, but no true ones. 



It occurs in small numbers (i to 4 per cent.), and variations are 

 of little diagnostic importance. 



B. Cells containing True Granules in their Protoplasm. 



I. Polynuclear Leucocytes (Plate VII., Fig. 7). — These are rather 



larger than a red corpuscle, and have a nucleus which is twisted 



