MAMMALIAN ANATOMY 
114 
preparations must be frequently made. Compare with the 
amphibian erythrocytes as to color, size, shape, and absence of 
nucleus. (This comparison may be made more conveniently and 
accurately if a mixed mount of human and amphibian blood in a 
drop of physiological salt solution be used.) By careful focusing, 
the thinner central region and thicker margin may be demon¬ 
strated. Note that the edge view exhibits a characteristic dumb¬ 
bell shape, although under perfectly normal conditions the 
erythrocytes have been found to be concavo-convex, resembling 
half of a hollow sphere. Note the collection of the erythrocytes 
into rouleaux. Draw a few erythrocytes from different aspects. 
Among the erythrocytes look for various kinds of leucocytes 
which, however, will be better distinguished from the stained 
preparations later. Note range of size, granules, nuclei. Draw 
a few leucocytes. 
2. Smear Preparations of Human Blood, for the Study of Leuco¬ 
cytes. 
Method of Preparation of Blood Smear. —The slide or cover- 
slip upon which the film of blood is to be spread should be abso¬ 
lutely clean and free from grease. “Bon Ami” is recommended 
as an effective cleaning agent. 
Take off directly upon the slide at about three quarters of an 
inch from one end, a drop of freshly drawn blood. Place the slide 
on the table and use a second clean slide as a spreader, by bringing 
one end of it in contact with the full width of the first slide on the 
side of the drop toward the middle of the slide and then slanting 
the spreader slide back toward the drop until, when it makes an 
angle of about 30° with the lower slide, it comes in contact with the 
drop which is thus made to flow across the slide in the angle 
between it and the spreader. The spreader, still held at an 
angle of 30° is then pushed steadily toward the opposite end of the 
slide, dragging the blood after it in the form of an evenly dis¬ 
tributed film upon the middle region of the slide. 
After spreading the film it should be carefully dried in air, 
care being taken not to allow anything to come in contact with 
it. Wright’s stain, which is a mixture of eosinate of methylene 
blue and eosinate of methylene azur in a nearly saturate solution 
