REFLEX ACTION 249 



include such phenomena as intestinal peristalsis, contraction and 

 dilatation of the pupil, certain mental operations, etc. In reality 

 most reflex acts are of a complex nature, involving associated 

 action on the part of several neurons and being manifested fre- 

 quently at several points. For example, a foreign body in the 

 larynx causes reflexly not only closure of the glottis, but also the 

 convulsive muscular contractions incident to coughing. The 

 realm of reflex action is obviously a wide one. 



It may be said that ordinary reflexes are usually under the 

 direction of the cord, but this does not imply that the brain may 

 not be concerned. Pricking the sole of the foot of a sleeping 

 person will cause him to draw up his leg without the interven- 

 tion of consciousness. Probably were he awake the withdrawal 

 would still be a reflex but he would certainly be conscious of 

 the pain, though after the act of withdrawal was accomplished. 

 Nor is reflex action by any means limited to the cerebro- 

 spinal system. Either of the two systems, or both, may be 

 concerned. 



Now in order for reflex movements to occur, there must be a 

 transference of impressions received by sensory cells to cells cap- 

 able of giving origin to motor impulses. The cells communi- 

 cate by their collaterals, which may be short or long, depending 

 on the distance between the cells concerned. Cells in the gray 

 matter of the cord are "connected" by such fibers, and they run 

 largely in the white matter of the cord joining cells on different 

 planes. They constitute the larger part of the anterior funda- 

 mental fasciculi, the anterior radicular zones, and the mixed 

 lateral tracts, and it is these paths which are mainly concerned in 

 reflex action of the cord. 



4. Augmentation. Sensory fibers, on reaching the cord, send 

 prolongations both upward and downward in the gray matter. 

 These prolongations, by their end arborizations, seem to com- 

 municate indirectly with several motor cells. In the simplest 

 reflex movements connected wi}h the spinal cord the muscular 



