20 
MAMMALIAN ANATOMY 
you have the cells under observation in the microscope field. 
When a clear conception of the shape of a given variety of cell 
has been gained, make a model of it in plastilina before attempting 
to draw individual cells. 
Finally record your study of each variety of cell by suitable 
drawings in which the form of the cell as seen from various aspects 
is shown. Make these drawings on a large scale so that the essen¬ 
tial parts of the cell, nucleus and cytoplasm, may be shown with 
whatever structural details may be peculiar to that type of cell. 
If the material is such that the arrangement of the cells with relation to 
each other is shown, this also should be studied and recorded. 
i. Cells from Animal Tissues. 
Epithelial Cells Scraped from the Inside of the Cheek. —Mount 
this material in a drop of physiological, or normal, salt solution 
(.6% to .8% sodium chloride in water, the percentage of this salt 
which occurs in animal tissues). Cover with a cover-slip as above 
directed, and examine first under low, then under high power, 
shutting down the illumination as may be needed to bring out 
well the details. Note the colorless, transparent nature of proto¬ 
plasm. The preparation may be stained on the slide under the 
cover-slip as follows: Place on the slide, in contact with the edge 
of the cover-slip, a drop of stain to be used, which must be in an 
aqueous medium when, as in this case, the material is in water or 
in an aqueous solution (methylene blue is frequently used for 
fresh or living material). At the opposite edge of the cover-slip 
lay a small fragment of filter paper with its edge in contact with 
the fluid in which the material is mounted, thereby drawing out 
this fluid and allowing the stain to enter. The excess of stain may 
be removed later by reversing the process. In any case supply 
some fluid at the edge of the cover-slip sufficiently frequently to 
prevent the preparation from drying. An aqueous solution of 
glycerine (50%) may be used to good advantage for this purpose, 
since it not only does not dry but also renders the preparation 
more transparent. 
Study the unstained and stained preparations to determine the 
shape and arrangement of the cells, seeking for this purpose cells 
in small groups of not more than four or five. Note the deeply 
