146 



THE CAPILLARIES. 



can be felt through the skin. It is known as theflutse. 

 The number of pulses in a minute, therefore, tells the 

 rate at which the heart is beating. 



FIG. 40. A small portion of the capillary network of the web between a frog's 

 toes, as seen with a microscope, a, a small artery feeding the capillaries; v, v, 

 small veins carrying blood back from the latter. The arrows indicate the direc- 

 tion of the blood-flow. 



23. The Capillaries (Fig. 40) are such tiny tubes that 

 they cannot be seen without a microscope. Their vast 

 number makes up for their small size; in most organs 



23. What is said of the size of the capillaries ? Of their number? 

 Illustrate. How does the blood do its work while flowing through 

 them ? Illustrate. 



