THE CENTRAL NERVOUS SYSTEM 373 



the strength of the induction currents is increased, 

 and (2) when the interval between the stimuli is 

 lessened. 



Segmental Arrangement of Reflex Apparatus. 

 1. Gently pass the seeker over the abdominal 

 walls on one side. 



The muscles in that region only will twitch. 



Kepeat the stimulus, but use a stronger 

 pressure. 



The area contracting will increase in extent 

 approximately in proportion to the increase in 

 the stimulus. The afferent nerves from any one 

 region are more closely related to the efferent 

 nerves of that same region than to those of other 

 regions. The fact that both afferent and efferent 

 fibres spring from the cord at the same level 

 suggests that their nerve cells lie also at approxi- 

 mately the same level. On increasing the stim- 

 ulus the afferent impulse spreads from segment 

 to segment of the cord. Further evidence of the 

 segmental arrangement will be gained by the 

 following experiment. 



2. With a clean, sharp knife make transverse 

 sections of the spinal cord, beginning in the cer- 

 vical region. A short time after each section 

 test the reflexes from the hind limb by mechani- 

 cal stimulation. 



