SOME MATTERS OF HYGIENE 391 



rather outside the present argument which is in support 

 of moderate rather than athletic activity. 



The vasomotor reactions which attend muscular con- 

 traction are perhaps sufficiently clear. The vessels of 

 the muscles are dilated and so are those of the skin . There 

 is probably an offsetting constriction in the digestive tract. 

 The adjustment becomes more positive and timely with 

 practice. The sedentary person lacks the capacity to 

 make this prompt adaptive change in the distribution of 

 the blood. His vasomotor system lacks resilience and 

 it cannot be relied upon to make strong corrective reac- 

 tions in the interest of health. 



The vasomotor effect of a cold bath is of a similar 

 nature. When the skin is chilled, the blood is sent to the 

 internal organs in increased quantity. This primary 

 diversion is the reverse of that when exercise is begun. 

 But it is followed by a hardening of the muscles ac- 

 companied by a heightened metabolism. The heat- 

 production of the body is augmented and when the 

 subject leaves the bath and begins to rub down there is 

 surplus heat to be thrown off. The vasomotor reaction 

 is then in the same direction as in exercise and the 

 occasion is really the same. * 



Muscular contractions directly promote the movement 

 of the blood aside from the enlistment of the heart in 

 their support, provided only that they are rhythmic 

 rather than sustained. When a muscle grows tense, it 

 thrusts the blood out of its own veins. Other veins are 

 caught and squeezed between neighboring muscles or 

 between muscles and the skin. The veins of the ex- 

 tremities, in which such action is most marked, are 

 provided with simple valves so placed as to allow no 

 backward movement of blood toward the capillaries. 

 Hence the emptying of these veins always drives blood 

 in the direction of the heart while they refill from the 

 tissues. This accelerating influence is lost when long- 

 sustained contractions are made, as in carrying a suit 

 case. 



