TEE SPINAL CORD AND REFLEX ACTIONS. 605 



far and wide no definite movement could result, for all the 

 muscles supplied from the cord would be made to contract, 

 and not morely those necessary to bend the index finger, for 

 example. We must here again, therefore, assume a path of 

 least resistance for the propagation of nerve impulses from a 

 given fibre coming down from the brain, to the efferent fibres 

 going to a certain muscle or group of muscles. The path 

 between the two is almost certainly not direct ; a co-ordinating 

 spinal centre intervenes, and all that the brain has to do is 

 to excite this centre, which then secures the proper muscular 

 co-ordination. If the hand be laid flat on the table and its 

 palm be rolled over, many muscles, including thousands of 

 muscular fibres, have to contract in definite order and sequence. 

 Persons who have not studied anatomy and who are quite 

 ignorant of the muscles to be used can perform the movement 

 perfectly; and even a skilled anatomist and physiologist, if 

 he knew them all and their actions, could not by conscious, 

 effort combine them so well as the cord does without such 

 direct interference. We have then to look on the cord as 

 containing a host of co-ordinating centres for different muscles.. 

 These centres are put in nervous connection, on the one hand,, 

 with certain regions of the skin, and, on the other, with regions 

 of the brain, and may be excited from either ; in the former 

 case the movement is called reflex ; in the latter it may be 

 reflex, or may be accompanied with a feeling of " will " and 

 is then called voluntary. The more accurately the required 

 centre, and no other, is excited, the more definite and precise 

 the movement. 



The Education of the Cord. Much of what is called edu- 

 cating our touch or our muscles is really education of the 

 spinal cord. A person who begins to play the piano finds at 

 first much difficulty in moving his fingers independently; the 

 nervous impulses from the brain to the cord radiate from the 

 spinal centres of the muscle which it is desired to move, to 

 others. But with practice the independent movements be- 

 come easy. So, too, the localizing power of the skin can be 

 greatly increased by exercise as one observes in blind per- 

 sons, who often can distinguish two stimuli on parts of the 

 skin which are so near together as to give only one sensation 

 to other people. Such phenomena depend on the fact that 

 the more often a nervous impulse has traveled along a given 

 road in the gray matter, the easier does its path become, and 



