LOCOMOTION 539 



In diseases which cause degeneration of the nerves going to a muscle, 

 stimulation causes results different from the above, and we get what is known 

 as the reaction of degeneration. 



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, how- 

 ever, 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 of motion or fulcrum. In a lever of 



f f Y 



j ! O 



A 



FIG. 337. 



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, andfulcmm 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 



