136 ELEMENTS OF PHYSIOLOGY 



any act, and no more. Ease of manner, as well as health, 

 make important the correction of conditions to which all 

 hurrying, ambitious persons are liable in an age of keen 

 competition and of ambition for learning and distinction. 

 Above all, repose of spirit and contentment of mind bring 

 grace and ease of body. 



230. Muscular Tone. That the muscles may be always 

 ready for use, they must not be entirely soft and flabby, 

 but under a condition of very slight contraction called tone. 

 We find that the muscular walls of the blood vessels possess 

 tone. It is this condition of slight contraction which causes 

 a wound in the flesh to gape open. If a tendon is cut, the 

 muscle shortens on account of its tone. If the nerve 

 going to the muscle is cut, the muscle lengthens a little, 

 that is, it relaxes, showing that there must be faint but con- 

 stant impulses coming through the nerve to keep the 

 muscle in tone. When one is asleep the body does not 

 lie perfectly straight, but the joints are slightly bent to 

 allow relaxation. 



231. THOUGHT LESSON. Physiology of the Circula- 

 tion. i. What do you notice after muscular exercise that 

 leads you to think that it makes the blood flow faster? 



2. What must be the effect in a vein when a contracting 

 muscle presses upon it ? Why does this aid the blood-flow 

 in only one direction ? 



3. What shows that exercise lessens the work of the heart ? 



4. Why is standing still more tiresome than walking ? 



5. Why is there need for valves in the veins ( 167)? 



6. Why is the activity of the kidneys greater in winter 

 than in summer, while with the skin the reverse is true 



(417)? 



232. Physiological Effects of Muscular Activity. It has 

 been explained how, during exercise, each muscle becomes, 

 as it were, a throbbing heart, squeezing the blood tubes 

 empty while contracting, and then relaxing and allowing 



