THE CIRCULATION. 71 



1. By its color. Venous blood is dark : arterial blood is 

 light. 



2. By the manner of its flow. Venous blood flows in a 

 steady stream, arterial blood in jets. 



11, The flow of blood from a vein stops more readily 

 than that from an artery. A bandage is commonly suf- 

 ficient. The arterial flow is more forcible. When the 

 blood spurts, it must be checked by firm pressure on the 

 vessel until a physician arrives. It may be necessary to 

 tie the artery. 



The pulmonary artery is peculiar because it carries 

 blue venous blood. The pulmonary veins carry red ar- 

 terial blood. In these respects they are exceptions to the 

 general rule. 



12. Arteries and veins are very strong. In experiments 

 made, they have borne a pressure equal to a weight of a 

 hundred pounds without bursting. But they sometimes 

 burst. In old age they become brittle. Certain diseases 

 make them brittle. 



THE PULSE. 



SECTION VI. 1. At a certain spot in the wrist, we can 

 feel a regular beat, which we call the pulse. A pulse may 

 be felt in several other places, but the wrist is the most 

 convenient. The pulse is a sudden rising-up of the wall 

 of the artery under the finger, and a slight stirring of the 

 whole artery in its bed. 



2. Every time the heart contracts, about six ounces of 

 blood are thrown into the arteries. These, being elastic, 

 stretch to receive it. Between the beats they contract, 

 forcing the blood along into the capillaries. 



This stretching is greatest in the aorta, close by the 



