THE BLOOD. 227 



it is thrown with great force, and urged on into the 

 farthest vessels. 



These are the feeders of the body, and when 

 they have supplied what is needful, they end in 

 minute veins, by which the blood is again brought 

 to the heart, which opens to receive it. 



This is the round of the circulation, which is 

 continued without stop or rest, and without any 

 wish or action of our own, our all-wise Maker 

 having placed it out of our control. This alternate 

 shutting and opening of our hearts produces that 

 motion in our arteries called the pulse. 



In childhood the heart beats upwards of a hun- 

 dred times in a minute ; in youth, about eighty, 

 and in manhood, from sixty to seventy. In 

 fevers and some other diseases, it also beats very 

 quickly. There is no pulsation in veins. 



The blood from which all our solid and fluid 

 parts are formed, when it is first drawn from a 

 vein or artery, looks like a simple liquid. After 

 it has stood, however, for a little while, it coagu- 

 lates, as it is termed, and separates into three very 

 distinct parts. When we look at it, we see a red 

 mass swimming in a straw coloured liquid. This 

 liquid is slightly viscid and salt to the taste, and is 

 called serum. The mass is made up of two bodies, 

 one a fine thready matter, which is named fibrin, 

 and the other of red globules, or little round bo- 

 dies. The fibrin, being heavier than the serum, 

 falls to the bottom' as it cools, and carries with it 

 the globules. 



