I 
BLOOD 
‘117 
perature during the transportation. Divide this into two parts. 
Set one portion aside, at ordinary room temperature, and, without 
disturbing it, observe from time to time during a period of half an 
hour or longer, the process of formation of the dark red clot, 
and its gradual shrinkage away from the sides of the container, 
leaving the yellowish serum as the liquid portion of the blood. 
Record your observations together with the exact time when each 
is made. Meanwhile, whip the second portion (25 c.c. or more) 
in a shallow evaporating dish, with a few twigs or broom corns, 
and note that as a result the formation of the threads of fibrin, 
which is an essential element in the process of clotting, is 
hastened, and that the agitation detaches the erythrocytes, which 
are normally held in the meshes of the fibrin, so that these remain 
in the serum when eventually the fibrin threads, clinging to the 
broom corns, are removed from the blood. Blood thus treated 
is known as defibrinated blood and remains indefinitely without 
clotting. 
2. Determination of the Proportions of Plasma and Cells in 
Freshly Drawn Blood. 
Use blood which has not begun to clot, or, if this is not avail¬ 
able, defibrinated blood (the latter will give the proportion of 
serum, rather than of plasma, to blood cells). Carefully measure 
a sample of the blood to be used, in the graduated tube of a 
centrifuge machine, and after subjecting it to the centrifuging 
process sufficiently to drive the blood cells, which are heavier 
than the plasma, to the bottom of the tube, determine the propor¬ 
tion of these by volume (approximately) by reading the gradua¬ 
tions corresponding to the various levels. Record. 
3. Specific Gravity of Blood. 
Determine the specific gravity of a drop of human blood by the 
following method: Place in a beaker a stock mixture of chloroform 
and benzol having a specific gravity of about 1055. Draw a drop 
of blood by the method already learned and shake it from the 
finger into the mixture. If it gradually sinks add chloroform 
drop by drop, stirring the mixture gently, until the drop of blood 
neither rises nor sinks but remains stationary at any level, thus 
