KINESTHESIA 333 



more important. Muscular action, reflex or voluntary, depends for its use- 

 fulness in nearly all cases upon its guiding coordination from the central 

 nervous system. In the complex voluntary actions of life especially one 

 sees the essential importance of these myo-tendo-articular impulses or 

 sensations, for skill, culture, and even civilization itself in part depend 

 on the fine adjustment of voluntary muscles in ever new and more delicate 

 ways. Imagine a "laborer" accustomed only to the rough use of the pick 

 and shovel in a trench, attempting to engrave a delicate monogram on 

 a small seal-ring. The inability in such a case might be due wholly to 

 the lack of this complex sense of delicate voluntary movement. These 

 conditions are present everywhere and always in our motor activities. 

 Take for another example the act of walking. This is almost a reflex 

 action in the person more than three years old. (See the description of 

 the process, page 392.) As one walks, continuous streams of impulses are 

 passing upward into the gray matter of several segments of the cord and 

 into the cerebellum and probably into the posterior and anterior central 

 cortex cerebri. These come from every part of every muscle and tendon 

 of the legs and from many of those of the trunk and neck engaged in the 

 body's equilibrium. From all the joints concerned (hip-joints, knees, 

 ankles, feet, spine, etc.) other sets of impulses pass similarly, and from 

 the skin, especially over the joints and wherever it comes in contact 

 with our garments. Moreover, we are kept dimly aware of the nature 

 of the path we walk, whether hard or soft or rough or smooth, by these 

 same sets of impulses. These too help reflexly to direct the spinal and 

 other centers in their complex task of control over these . multifarious 

 walking-parts. One may similarly trace the same process in speaking, 

 swallowing, chewing, and numerous other movements, as well as in 

 thousands of purely voluntary actions known to the many trades, occupa- 

 tions, and amusements. It is, in short, only on the information furnished 

 by these numberless incoming messages that the centers directing move- 

 ment can do their work. When we make voluntary movements, espe- 

 cially with the arms and hands, the eyes usually follow the movements 

 and we are apt to think that it is by vision that they are directed. They, 

 however, can be made even better in many cases after some practice, 

 without any use of the eyes whatever. Unless there were sent into the 

 kinesthetic centers information of an exact nature concerning the relative 

 degree of contraction of each muscle-fiber, these central motor cells 

 could not properly actuate the muscles. A partly contracted fiber, for 

 example, would need a different degree of stimulus from one contracted 

 fully. Not only must a number of different muscles be made to contract, 

 but each one often in a particular way, hard enough but not too hard 

 and each at exactly the right time and for exactly the right period. 

 In short, a maze of relations exists which would make of a movement 

 not thus minutely directed by afferent messages a mere jerk or con- 

 vulsion. Never would we have the wonderfully adapted, perfect, and 

 certain action we are familiar with. The concertos of de Pachmann 

 differ from the drumming of our fair but misguided neighbor in the next 



