158 THE HYGIENE OF THE CIRCULATION 



beat. As the pressure in the arterial system is lowered 

 by the draining away of blood through the active organs, 

 the heart is made to work more quickly, in order to pump 

 the blood faster into the arteries. The arteries are 

 thereby kept well filled and the blood pressure main- 

 tained at a height sufficient to drive the blood through 

 all the tissues in adequate amounts. In this way, the 

 adjustment of the blood supply to the needs of all the 

 organs, including the brain, is made possible within the 

 limits of normal activity. 



Faulty distribution. When, however, the body 's nor- 

 mal activity is exceeded, as when large numbers of 

 muscles are used at once, both of these methods of 

 adjustment may be inadequate and the blood may be 

 drained out of the arteries faster than the heart can 

 pump it in. The blood pressure then becomes so low 

 that the blood is not forced in sufficient amounts to the 

 brain. The result is dizziness and faintness. Such faulty 

 distribution undoubtedly accounts for the fainting of 

 athletes after a hard run or row. In cases of stomach and 

 intestinal irritation which leads to the abnormal dilata- 

 tion of the abdominal blood-vessels, the arterial blood 

 pressure is similarly lowered, and as a result faintness 

 and dizziness are common accompaniments of these ill- 

 nesses. Similar effects are also produced by considerable 

 losses of blood, or hemorrhage. 



Effects of eating. These facts make it clear why it 

 is unwise to attempt severe brain or muscular work after 

 a hearty meal. The drowsiness which accompanies the 

 brain work shows that the brain is not getting its full 

 share of blood because of the activity of the digestive 

 organs. In the case of hard muscular work, the reverse 

 is true. The muscles draw the blood to themselves and 

 so digestion is delayed. 



