524 



THE NERVOUS SYSTEM 



the ganglion and the cord the central part degenerates and the peripheral 

 is unaffected. 



Spinal Reflexes in Man and Mammals. Much of our knowledge of 

 the reflexes of the cord is derived from experiments on dogs, though paral- 

 ysis of the lower extremities in man, by accident or otherwise, has given con- 

 firmatory information. In man the spinal cord is so much under the control 

 of the higher nerve centers that its own individual functions in relation to re- 

 flex action are apt to be overlooked. But if the skin of the foot is stimulated, in 

 a man whose lumbar cord is completely separated by injury or disease, the 



FIG. 368. Scheme of the Relation of the Posterior Root Fibers upon Entering the Cord. A, The 

 branch of the dorsal root fibers upon entering cord; B, terminal arborization about cell bodies 

 of the cord; DR, axones of the dorsal root ; B, their ascending and descending branches; C, 

 collaterals. (After Cajal.) 



foot will be drawn away from the stimulus; or, if the stimulus be strong 

 enough, the entire leg will be moved. In both cases the movement may be 

 orderly and well coordinated, and shows that the sensory stimulus has pro- 

 duced a coordinated reflex through the lumbar cord. The injured person 

 feels no sensation of pain nor of action, and the phenomenon is independent 

 of the higher nerve regions. The stimulus that is applied to man must be 

 carefully graded, since when too intense it calls forth muscular spasms or 

 convulsive action. 



