60 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



own spinal motor cell and cerebral motor cell, and the 

 sensory cells in the cerebrum and in the cord to com- 

 municate each with its corresponding motor cell. Thus, 

 every cerebral sensory cell would have its correspond- 

 ing terminal on the body surface, with a connecting fiber 

 between, passing through a corresponding spinal sen- 

 sory cell; and every cerebral motor cell its correspond- 

 ing spinal motor cell and muscular terminal with a con- 

 necting fiber between. Now touch a point on the body 

 surface, and a wave or current of influence is carried 

 along a sensory fiber through the cord, as already ex- 

 plained, to a cerebral sensory cell, awakening conscious- 

 ness there. Immediately, or perhaps only after delib- 

 eration, the influence is transferred by a connecting 

 fiber to a cerebral motor cell, awakening will, and by 

 it down the spinal cord by a motor fiber, and out to a 

 muscle determining appropriate motion. 



See, then, all the phenomena in a case of simple re- 

 sponse to external impression : (i) Impression ; (2) trans- 

 mission inward ; (3) change in a sensory cell — conscious 

 sensation ; (4) transmission to a motor cell ; (5) change 

 in the motor cell — will; (6) transmission outward along 

 a motor fiber ; (7) contraction of a muscle. Metaphor- 

 ically we might say that we have here a complex instru- 

 ment of communication between the external world and 

 the conscious self, with the self playing on brain cells or 

 interior nerve terminals at one end, and the external world 

 playing on exterior nerve terminals at the other end. 



In Reflex Action. — If the impression is on an interior 

 surface in a normal condition, the current of influence 

 on reaching the spinal sensory cell is transferred across 

 by short circuit to the corresponding spinal motor cell 

 and reflected immediately back along a corresponding 

 motor fiber to the appropriate muscle, without rising at 

 all into consciousness. Such is the case in impressions 



