206 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



film for a quarter of a minute, wash it, and then examine it under 

 the low power of the microscope. If the film is properly stained, 

 the nuclei of the leucocytes will be seen as blue points, which can 

 be distinguished with great ease with the |-inch objective. If 

 they are not visible, the methylene blue must be applied for about 

 a quarter of a minute more and the examination repeated. 

 When the nuclei are seen to be well stained the film is dried 

 and mounted. 



This process gives results which resemble those afforded by 

 Jenner's stain, except that the fine eosinophile granulations in the 

 polymorphonuclear cells are always less obvious and often quite 

 invisible. It is also suitable for malarial parasites and bacteria. 



The practitioner is recommended to practise this method of 

 staining, as it does not require any reagents which are not to be 

 found in every well-stocked surgery. The watery solution of 

 methylene blue which is used as a counterstain for the tubercle 

 bacillus and some red ink are all that are necessary. 



DIFFERENTIAL LEUCOCYTE COUNT 



The following varieties of leucocytes are to be recognised, 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. 



