THE BLOOD. 157 
to estimate the total quantity of blood in the body of an animal 
by bleeding is highly fallacious for various reasons. It is im- 
possible to withdraw all the blood from the vessels by merely 
opening even the largest of them, and, if it were, the original 
quantity would be augmented by fluid absorbed into them dur- 
ing the very act. No method has as yet been devised that is 
free from objection, hence the conclusions arrived at asfto the 
total quantity of blood are not in accord; and in the nature of 
the case no accurate estimate can be made, but about one thir- 
teenth to one fourteenth may be taken as a fair average; so that 
in a man of one hundred and forty pounds weight there should 
be about ten pounds of blood; but, of course, this will vary 
with every hour of the day and will be greatest after a meal. 
As an example of the methods referred to, we give Welck- 
er’s, which is briefly as follows: The animal is bled to death 
from the carotid; a sample of the defibrinated blood (1 cc.) is 
saturated with carbon monoxide (CO), which gives a perma- 
nent red color; this diluted with 500 cc. of water furnishes a 
standard sample. The blood-vessels of the animal are washed 
out with a ‘6 per cent solution of common salt, but the out- 
' flowing stream is colorless; to this is added the fluid obtained 
by chopping up the tissues of the animal, steeping, washing 
out, and pressing. The whole is diluted to give the color of the 
standard solution, from which the amount of blood in this mixt- 
ure may be calculated, since every 500 cc. answers to 1 cc. of 
blood; the blood obtained by bleeding can, of course, be accu- 
rately measured. 
It would be slightly more accurate to make the diluted 
blood of the animal operated upon the standard without treat- 
_. ment with carbon monoxidg,. aoe 
~ .» Such a method, though the best yet devised, is open to ob- 
jection also, as will occur to most readers. # 
The relative quantities of blood in different parts of the 
body have been estimated to be as follows: 
LIV GT taknauanGred ate. auees. sees one fourth. 
Skeletal muscles..........0c0ceee eens S 
Heart, lungs, large arteries, and veins. 
Other structures,.... 0... cece cece 
The significance of this distribution will appear later. 
The Coagulation of the Blood.—When blood is removed from 
its accustomed channels, it undergoes a marked chemical and 
physical change, termed clotting or coagulation. In the case 
of most vertebrates, almost as soon as the blood leaves the ves- 
“ee “cc 
its c<3 
