THE SUMMERING OF HUNTERS. I3l 



in its entirety, but only some parts of it leave the 

 vessels. The parts of the blood which leave the 

 bloocl-stream and saturate the tissues must, after a 

 time, return to the blood-stream ivitJdn the blood- 

 vessels again. So that we have here two pro- 

 cesses — the process of leaving the blood-vessels and 

 the process of returning to the blood-vessels. There 

 are three divisions of blood-vessels : (1) arteries 

 which convey the blood in a compact stream ; 

 (2) capillaries, of less than hair-like minuteness, 

 which are terminations of the arteries, and through 

 which the blood meanders; and (3), veins or the 

 blood-vessels which receive the blood after it has 

 been permeating and saturating the tissues, and 

 convey it back again to the heart. Now the blood 

 escapes through the delicate walls of the capillary 

 blood-vessels and finds its way into the blood-stream 

 by a system of vessels called " absorbent vessels." 

 When the blood leaves the capillaries for the tissues 

 it is scarlet with oxygen and rich particles for the 

 repair of the tissues ; but when it finds its way 

 through the absorbents into the veins it is dark 

 purple almost— in other words, it has given up its 

 oxygen and rich materials to the tissues, and the 

 tissues have in return loaded it with their refuse. 



Just one other point. The blood is propelled 

 powerfully through the arteries of the body by the 

 contraction of that powerful hollow muscle called 

 the heart. Here is a force-pump that we can see, 

 and we can measure the force of the flow of the 



K 2 



