112 ELEMENTS OF APPLIED MICROSCOPY. 



basophiles or lymphocytes are about the size of the 

 red corpuscles, robin's egg blue in color with a round 

 dark-blue nucleus and a few fine dark-blue granules. 

 Large mononuclear basophiles are three times the size 

 of the red cells and pale blue with a large oval blue nucleus. 

 The third type, the neutrophiles, are intermediate between 

 the red-granuled eosinophiles and the blue-granuled 

 basophiles. They are polymorphonuclear, twice the 

 size of the erythrocytes, and blue, with one or more 

 darker lilac-colored nuclei of a twisted shape and numer- 

 ous medium-sized granules of a reddish-lilac color. 

 Blood-plates are almost always seen, purplish rounded 

 or oval bodies one-third the size of the erythrocytes, 

 with irregular edges and iine blue mottlings. In patho- 

 logic conditions numerous other cell elements may be 

 present. Most of these cell elements are seen in Fig. 44. 

 Such a stained preparation as that described is used for 

 the study of the structure of the blood-cells and for the 

 determination of the relative number of white cells of the 

 various types. A differential blood count, as it is called, 

 is made by counting several hundred white cells and 

 calculating the percentage of each form. For thus de- 

 termining the absolute number of the blood corpuscles the 

 apparatus called a hsemocytometer is designed. It con- 

 sists of a glass slide containing a cell of known diameter 

 and a depth of o.i mm., on the bottom of which is ruled 

 a micrometer scale marking off squares 0.025 rnm- on a 

 side. The blood is diluted, in a special pipette constructed 

 for the purpose, with 100 parts of Gower's solution 

 (100 cc. water, 15 cc. acetic acid, 6 g. sodium sulphate), 



