1 50 Life and Health 



The blood brought to the capillaries of the stomach, 

 intestines, spleen, and pancreas is gathered into veins 

 which unite into a single trunk called the portal vein. The 

 blood, thus laden with certain products of digestion, is 

 carried to the liver by the portal vein, mingling with that 

 supplied to the capillaries of the same organ by the hepatic 

 artery. From these capillaries the blood is carried by small 

 veins which unite into a large trunk, the hepatic vein, which 

 opens into the inferior vena cava. 



The portal circulation is thus not an independent system, 

 but forms a kind of loop on the systemic circulation. 



Experiment 64. To illustrate the action of the heart, and how it 

 pumps the blood in only one direction. Take a household rubber 

 bulb syringe of any standard make. Sink the suction end into water 

 and press the bulb. As you let the bulb expand, it fills with water ; 

 as you press it again, a valve prevents the water from flowing back, 

 and it is driven out in a jet along the other pipe. The suction pipe 

 represents the veins ; the bulb, the heart ; and the tube end, out of 

 which the water flows, the arteries. 



228. The Rhythmic Action of the Heart. To maintain a 

 steady flow of blood throughout the body the action of the 

 heart must be regular and methodical. The heart does not 

 contract as a whole. The two auricles contract at the same 

 time, and this is followed at once by the contraction of the two 

 ventricles. While the ventricles are contracting, the auricles 

 begin to relax, and after the ventricles contract they also relax. 

 Now comes a pause, or rest, after which the auricles and ven- 

 tricles contract again in the same order as before, and their 

 contractions are followed by the same pause as before. This 

 cycle of changes is known as the rhythmic action of the heart. 



*/ 229. The Beat, or Impulse, of the Heart. If the hand be 

 laid flat over the chest wall on the left, between the fifth 

 and sixth ribs, the heart will be felt beating. This move- 

 ment is known as the beat, or impulse, of the heart, and can be 



