LOCOMOTION 475 



The intensity of the anodic or cathodic effects is increased by using small 

 electrodes, and decreased by electrodes of large surface. In fact in practice 

 it is usual to apply the indifferent electrode to an extended surface, thus re- 

 ducing its effect below the stimulating intensity. This gives only one active 

 stimulating electrode and is known as the method of unipolar stimulation. 



SOME SPECIAL COORDINATED MOTOR ACTIVITIES. 



I. LOCOMOTION. 



The greater number of the more important muscular actions of the human 

 body, those, namely, which are arranged harmoniously so as to subserve some 

 definite purpose in the animal economy, are described in various parts of this 

 work in the sections which treat of the physiology of the processes by which 

 these muscular actions are resisted or carried out. There are, however, some 

 very important and somewhat complicated muscular acts which may be best 

 described in this place. 



Walking. The coordinated movements of the body are carried out 

 by the skeletal muscles acting on the skeletal elements as a system of levers. 

 Even the bones of the skull are levers in so far as their relations to muscles 

 are concerned. 



Examples of the three orders of levers in the Human Body. All levers have been 

 divided into three kinds, according to the relative position of the power, the weight to be 

 moved, and the axis oj motion or fulcrum. In a lever of the first kind the power is at one 

 extremity of the lever, the weight at the other, and the fulcrum between the two. If the 

 initial letters only of the power, weight, and fulcrum be used, the arrangement will stand 

 thus: P. F. W. A poker as ordinarily used, or the bar in figure 337, may be cited as an 

 example of this variety of lever; while, as an instance in which the bones of the human 



FIG. 337. 



skeleton are used as a lever of the same kind, may be mentioned the act of raising the body 

 from the stooping posture by means of the hamstring muscles attached to the tuberosity 

 of the ischium or of the triceps which extends the forearm by action at the elbow, 

 figure 337. 



