ed to the last tumbler make a comparative study of all.
Note that coagulation begins in all parts of the liquid at the same time
and that, as the process goes on, the clot shrinks and is drawn toward the
center.

4. Place a clot from one of the tumblers in experiment 3 in a large vessel
of water. Thoroughly wash, adding fresh water, until a white, stringy
solid remains. This substance is fibrin.

5. Examine the coagulated blood obtained from the butcher (bottle 2).
Observe the dark central mass (the clot) surrounded by a clear liquid (the
serum). Sketch the vessel and its contents, showing and naming the parts
into which the blood separates by coagulation.

*To examine the Red Corpuscles.*--Blood for this purpose is easily obtained
from the finger. With a handkerchief, wrap one of the fingers of the left
hand from the knuckle down to the first joint. Bend this joint and give it
a sharp prick with the point of a sterilized 'needle just above the root
of the nail. Pressure applied to the under side of the finger will force
plenty of blood through a very small opening. (To prevent any possibility
of blood poisoning the needle should be sterilized. This may be done by
dipping it in alcohol or by holding it for an instant in a hot flame. It
is well also to wash the finger with soap and water, or with alcohol,
before the operation.) Place a small drop of the blood in the middle of a
glass slide, protect the same with a cover glass, and examine with a
compound microscope. At least two specimens should be examined, one of
which should be diluted with a little saliva or a physiological salt
solution.(16) In the diluted specimen the red corpuscles appear as
amber-colored, circular, disk-shaped bodies. In the undiluted specimen
they show a decided tendency to arrange themselves in rows, resembling
rows of coins. (Singly, the corpuscles do not appear red when highly
magnified.)

A few white corpuscles may generally be found among the red ones in the
undiluted specimen. These become separated by the formation of the red
corpuscles into rows. They are easily recognized by their larger size and
by their silvery appearance, due to the light shining through them.

*To examine White Corpuscles.*--Obtain from the butcher a small piece of
the neck sweetbread of a calf. Press it between the fingers to squeeze out
a whitish, semi-liquid substance. Dilute with physiological salt solution
on a glass slide and examine with a compound micros