XV. BLOOD 
A. HISTOLOGY OF BLOOD. 
i. Examination of Fresh Blood. 
Amphibian Blood. —This may be obtained from a freshly 
killed specimen of Necturus or from the cut surface left by snip¬ 
ping off the toe of a living frog. 
Add a little of the blood to a drop of physiological salt solution 
upon the middle of a clean slide, and cover at once with a clean 
cover-slip. Examine first under low power, then under high 
power, of the compound microscope. Note the erythrocytes, 
their color, shape as seen lying flat and also upon edge, shape and 
position of nucleus. Draw flat and edge views. Note the far less 
numerous leucocytes, with their varying sizes, granular cytoplasm, 
pseudopodia, and nuclei. Watch a single leucocyte for 5 minutes 
making sketches of it at half-minute intervals to detect amoeboid 
activity. 
Human Blood. —This may be conveniently obtained and 
mounted as follows: Prepare two clean cover-slips. Sterilize 
the surface from which blood is to be drawn (the skin of the finger 
at the base of the nail, the ball of the finger, or the lobe of the ear) 
by washing thoroughly with 70% alcohol applied by means of a 
little absorbent cotton. After the surface has dried do not allow 
anything to come in contact with it until the incision has been 
made. Sterilize a clean, sharp needle or lance by rubbing it 
thoroughly wdth a little cotton wet with 70% alcohol. Allow it 
to dry. Make a quick cut deep enough to allow the blood to flow 
out freely, press slightly to start the blood, but do not continue 
to use pressure. Place a drop of the blood thus obtained upon one 
of the cover-slips. Immediately apply the other cover-slip to 
this, thus spreading the blood in a thin film. Lay this double 
cover-slip wdth the film of blood between, upon a glass slide and 
examine it first under low, then under high power. Note the 
erythrocytes, rapidly losing their smooth outline which becomes 
indented at regular intervals (crenated). On this account fresh 
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