IRRITABILITY 117 



;art is stimulated to beat faster, if it rises, to beat more 

 lowly. If a muscle is active the blood vessels that go 

 to it are stimulated. They enlarge and carry more 

 )lood to it. After violent exercise when a great deal 

 )f heat has been set free by the activity of the muscles 

 le surface blood vessels in the skin are stimulated and 

 ley enlarge. Also the sweat glands are stimulated to 

 ictivity and an increase in perspiration follows. If the 

 >kin loses heat through sudden or prolonged constriction 

 )f the surface blood vessels one is apt to feel cold and 

 driver. Shivering is a spasmodic contraction of the 

 muscles. The heat thus produced compensates for that 

 which has been lost and tends to produce a feeling of 

 warmth. 



Exercise. — Exercise is an important factor in the 

 health of the body. It is a natural form of massage. 

 It involves the disintegration and reformation of pro- 

 toplasm, the kneading of the blood vessels, a quicker 

 heart action and deeper respiration. Thus it facilitates 

 the intake of oxygen and the carrying off of waste 

 products. It must, however, be of the proper sort and 

 must be taken in moderation, and with due regard for 

 times and s'easons. Exercise should not be taken too 

 soon after eating because the blood circulates rapidly 

 through the exercised parts, the blood vessels there be- 

 come enlarged and draw blood away from the stomach 

 where it is due at that time. 



Curiously enough either too much exercise or too 

 little has exactly the same effect — a lack of oxidation. 

 In both cases disintegration of complex substances 

 in the muscle takes place in excess and oxygen is 



