THE CIRCULATORY SYSTEM. 57 



veins. Their name comes from a Latin word which 

 means a hair. It is difficult to imagine how numer- 

 ous these little capillary blood-vessels are, and bow 

 v w^ll they are distributed to all parts of the body. 

 You could scarcely prick your skin with a needle 

 anywhere without bringing some blood to the sur- 

 face ; you are sure to pierce some capillary and cause 

 it to leak. 



In the capillaries are the landing 



Blood Change 



in the places where the little cargoes of 



capillaries. bui lding ma terial, which have been 

 floated from the port of the heart through the arte- 

 rial rivers, are unloaded and distributed to the thou- 

 sands of little working cells, which are everywhere 

 busy in building or repairing the body. At some 

 places material for muscle is unloaded; at others 

 material for bone, nerve or finger nail is wanted. In 

 exchange for this new material which the capillaries 

 distribute to the body, they take back from the body 

 the material which has become old, worn out, and 

 unfit for use. The consequence is that the blood 

 which has come from the arteries into the capillaries 

 red and pure, leaves them and gathers in the veins, 

 dark and impure. It would be altogether unfit to 

 make another round through the body without being 

 purified; so the capillaries deliver it to the veins, 

 and these carry it to the heart, which drives it to the 

 lungs one of the organs of another system where 

 its worn-out matter is unloaded, and it is again made 

 fit to feed the body. 



