FAINTING. 265 



muscles into play ; but if the mind is still intent upon the 

 line of work maintained throughout the day, the exercise may 

 prove of little benefit. He may return more tired than when 

 he set out. The exhilaration of horseback riding may prove 

 far better, though perhaps involving much less musculai 

 exertion. 



During fatigue the cell-bodies are found to decrease in 

 size, but there is no discernible change in nerve fibers as a 

 result of fatigue. 



It is worthy of note that in fasting the nervous tissue is 

 less reduced than any other tissue, being scarcely diminished 

 by complete starvation. 



Blood is supplied to the brain through four arteries, the 

 right and left Internal Carotid arteries, and the right and left 

 Vertebral arteries. These arteries are so connected by cross 

 branches that if any three of them should be compressed, 

 or the blood-flow in them otherwise stopped, the fourth would 

 still be able to give the brain blood enough for its work. 



If the supply of blood to the brain is shut off, uncon- 

 sciousness quickly follows. In the ordinary faint the blood 

 supply has been reduced, owing to the diminution of the 

 blood pressure or heart's force. It may be due to inhibition 

 of the heart from some emotion, or bad odor, as in a close 

 room ; severe pain may be the cause; a blow over the pit of 

 the stomach may stop the heart by reflex action. Fresh air 

 should be supplied, and the body laid flat on the back. This 

 position makes it easier for the blood to reach the brain and 

 restore consciousness. Smelling salts (or ammonia) may stim- 

 ulate respiration and circulation. Sprinkling a little cold 

 water on the face may have the same effect, but it is not ne- 

 cessary to pour a large quantity of water over the person. 

 Rubbing the limbs toward the heart promotes the flow of 

 blood, and tends to start the heart to activity. 



