THE BLOOD OF ANIMALS. 
101 
variations, increasing rapidly after a meal, and falling as 
rapidly. 
There is less blood in cold-blooded than in warm-blood¬ 
ed animals; and the larger the animal, the greater is the 
Fig. C6 .— Capillary Circulation in the Web of a Frog’s Foot, X 100 : a, b, small veins ° 
d, capillaries in which the oval corpuscles are seen to follow one another in sin¬ 
gle series; c, pigment-cells in the skin. 
proportion of blood to the body. Man has abont a gallon 
and a half, equal to one thirteenth 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- 
