Ir2 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 fine 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 hemocytometer is designed. It con- 
sists of a glass slide containing a cell of known diameter 
and a depth of o.1 mm., on the bottom of which is ruled 
a micrometer scale marking off squares 0.025 mm. 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), 
