THE NEUROMUSCULAR MECHANISM 93 



We need not refer to unusual or pathologic examples to 

 confirm the impression that the degree of command ex- 

 erted by the nervous system varies very widely indeed. 

 The most energetic responses are probably those produced 

 when a number of afferent channels are simultaneously 

 used to promote movements which could be reflexly 

 evoked in connection with either one of these paths. 

 Camis 1 has shown that in the lower animals it is possible 

 to secure more powerful reflex contractions by stimulating 

 two sensory nerves at once than can be caused to occur by 

 the most intense excitation of either of these paths by 

 itself. Some would interpret this result to mean that the 

 same perikarya are more strongly stimulated when the 

 approach is made through the larger number of afferent 

 fibers; others would infer that a larger number of motor 

 neurons are made accessible to the influence of the stimu- 

 lation. Possibilities like these will receive additional dis- 

 cussion when we reach the subject of fatigue and its 

 postponement. 



Coordination. This word has already been said to be 

 so comprehensive that it can be made to express the main 

 function of the entire nervous system. It must now be 

 viewed with especial reference to the execution of muscular 

 movements. We seldom call into voluntary action a 

 single muscle quite unaffected by any other. The use of 

 solitary muscles in pure reflexes is equally rare. In the 

 vast majority of cases, though we may be able to select 

 one muscle as the chief performer, we have to recognize 

 the auxiliary part played by its fellows in carrying out 

 even what seems a simple movement. It is theoretically 

 possible to bend the elbow by contracting a single muscle, 

 the biceps humeri, but in executing the act in the habitual 

 manner we find that the other muscles of the arm are not 

 passive, but are changing their tension in such a way as to 

 give steadiness, precision, and economy of force to the 

 whole proceeding. Certain ones directly reinforce the 

 essential movement, others assist indirectly by making 

 1 Journal of Physiology, 1909, xxxix, 228. 



