284 THE HUMAN MECHANISM 



with use. The use of a nervous mechanism is generally 

 essential to its proper development, just as the use of a 

 muscle is essential to its strength. If the child never tried to 

 walk, the neurones which carry out the movements of walk- 

 ing would not develop ; not only do the muscles of an arm 

 strapped down to the side of the body waste away and be- 

 come practically bands of connective tissue, but the neurones 

 concerned in the actions which the arms should execute 

 degenerate and may ultimately be irreparably injured. 



Provision is made from earliest life for the proper develop- 

 ment of these neurones and the establishment of irritable 

 connections between them by use; out of the first aimless 

 movements of the head and eyes and hands and legs of the 

 baby the simpler coordinating nervous mechanisms are one 

 by one brought to perfection ; then comes the training of 

 those reflexes which maintain the erect position and of those 

 nervous mechanisms which govern locomotion; then play 

 comes in, with its ceaseless activity, increasing still further 

 the number of movements which the nervous system can 

 make and correspondingly enlarging the possibility of human 

 achievement. As the child grows older the family calls 

 upon him to contribute some share to its life or support; 

 new activities, in the shape of chores about the house or the 

 farm, now share with play the work of the nervous system ; 

 activity becomes less general, more special. Finally the 

 youth settles down to some definite occupation or pursuit, 

 and the more strictly this is adhered to, the narrower be- 

 comes the range of activity; the more constantly a few sys- 

 tems of neurones are used, the more rarely are others called 

 into play. 



18. The physical basis of habits. All this indelibly writes 

 its history in the nervous system. No fact is more significant 

 or of greater physical and moral import than that the doing 

 of any act so affects the connections of neurones with one 

 another as to make it easier to do the same act again under 



