292 MUSCLES 



pivot, and this forward fall is stopped only by swinging the 

 flexed leg forward and allowing the foot to strike the 

 ground some distance ahead. Then, the body weight is 

 shifted to this foot and the operation is repeated with the 

 other leg. In ordinary walking not only the leg flexors are 

 used but also those of the toes and foot, and the body is 

 usually more or less bent at the waist while the arms swing 

 freely about the shoulder sockets. The feature of this 

 combination of movements which makes it difficult to the 

 child is that these various movements must be so correlated 

 that they take place in regular sequence, and the power to 

 do this comes only with complete nerve control. 



Rimning differs from walking in that the advancing foot 

 alights on the toes alone, and there are instants when 

 neither foot is in contact with the ground. The body is 

 bent more, the pressure of the toes thrusts the body forward 

 with more force and the rate of action of all the muscles is 

 more rapid. Accompanying this greater rapidity of action 

 is a greater demand for oxygen on the part of the muscles, 

 and a consequent increase in the rate of breathing. For 

 this reason running forms a valuable type of exercise for 

 the development of the lung power and as a stimulant to 

 circulation. 



Effect of alcohol upon muscular activity. — The exact 

 efl^ect of alcohol upon muscle action is not yet fully deter- 

 mined. Sufficient evidence has been collected, however, 

 to show that the combined action of alcohol upon the mus- 

 cle cells and upon the nerve centers which control these 

 cells is such as to make it less valuable than other fuel 

 foods for the production of energy and activity. And it 

 has been shown further that while the immediate effect of 

 small doses may result in temporary stimulation, this period 



