THE BLOOD OF ANIMALS. 101 
proportion of blood to the body. Man has about a gallon 
aud a half, equal to one-tenth of his weight. The heart of 
the Greenland Whale is a yard in diameter. 
The main Office of the Blood is to supply nourish- 
ment to, and take away waste matters from, all parts of 
the body. It is at once purveyor and scavenger. In its 
circulation, it passes, while in the arterial half of the cap- 
illaries, within an infinitesimal distance of the various tis- 
sues. The plasma, carrying the nutritive matter needed, 
exudes through the walls of the capillary tubes; the tissue 
assimilates or makes like to itself whatever is suitable for 
its growth and repair; and the lymphatics (the escape- 
pipes) take up any surplus, and return it to the blood. 
At the same time, the venous part of the capillary. net- 
work absorbs the waste products of the tissues, expelling 
the gases by the lungs, and the solid matters by the skin 
and kidneys. The special function of the several constit- 
uents of the blood is not clearly known. The colorless 
corpuscles in Vertebrates are supposed to be the source of 
the red disks. The latter are probably the carriers of 
gases, absorbing oxygen in the lungs, which they give to 
the tissues, and receive carbonic acid in exchange. 
Like the solid tissues, the blood, which is in reality a 
liquid tissue, is subject to waste and renewal, to growth 
and decay. Its source is the product of digestion, not 
only the lacteal chyle, which is the only fluid in the body 
that has never formed part of the blood, but also the 
chyme absorbed by the blood-vessels of the stomach. 
Chyle differs from blood chiefly in containing less albu- 
men and fibrine, and no red disks. The transmutation is 
accomplished by the small glands (mesenteric) attached to 
the lacteals, the lymph, and the lungs. In the low organ- 
isms, the nutritive fluid is prepared by contact with the 
tissues, without passing through special organs. 
