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 about 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, w r hile 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- 



