36 THE: BEGINNINGS OF LIFE. 



in texture, and that are shielded in an unusual manner 

 from disturbing forces, except at their two extre- 

 mities V On the one hand, these fibres connect peri- 

 pheral parts with the nerve-centres, whereby such parts 

 are rendered sensitive j whilst, on the other hand, the 

 nerve-centres are also in connection with other sets of 

 nerve-fibres which are accustomed to transmit stimuli 

 outwardly towards the muscles in which they are dis- 

 tributed, so as to call them into activity. The expe- 

 riments of Phillipeaux and ; Vulpian have abundantly 

 confirmed the reasonings of Mr. G. H. Lewes 2 , which 

 went to show that there was no real difference in pro- 

 perty between the so-called sensory and motor nerves. 

 The fundamental property of each alike is the capa- 

 bility of transmitting a stimulus, and for this property 

 Mr. Lewes proposed the name neurlUty. Neurility, 

 therefore, is the characteristic property of a nerve, just 

 *as contractility is the characteristic property of a muscle ; 

 and the different results produced, when a sensory and 

 a motor nerve respectively are stimulated, is due to the 

 different nature of the organs to which the stimulus is 

 directed. When the stimulus traverses the nerve in 

 an afferent direction, this, impinging upon a nerve- 

 centre, liberates a larger or smaller quantity of energy, 

 and may produce what is called a sensation ; but when, 

 on the other hand, a stimulus originating in a nerve- 

 centre is propagated in an efferent direction, then this 



1 'Principles of Psychology,' 1869, No. 20, p. 24. 



2 ' Physiology of Common Life,' 1859. 



