THE LIVING WORLD 2^5 



each and all of the powers possessed by inorganic bodies. 

 The processes of growth and generation are different 

 indeed from the activities of non-living bodies, but far 

 more divergent is the power of feeling, of perceiving by 

 the senses surrounding objects, and of regulating bodily 

 actions in conformity thereto. Sensitivity is the special 

 attribute of nervous tissue, and each creature's nervous 

 system is thus an organ of intervention between it and 

 the world around it. 



Sensation can be absolutely known only to the being 

 that experiences it; nevertheless it would be in the 

 highest degree absurd not to be certain that a cat feels, 

 sees, hears, smells, and tastes, and that it possesses feelings 

 of pleasure and pain, with propensions, desires, and 

 emotions of affection, fear, animosity, &c. But different 

 parts of the nervous system have different functions, as 

 is the case with different parts of one portion of it. 

 Thus part of the spinal cord transmits an influence up- 

 wards to the brain, resulting in sensation, while another 

 part transmits an influence downwards from the brain, 

 resulting in movement. The ascending sensitive in- 

 fluence passes to the cord through the posterior roots of 

 the spinal nerves into which enter the nervous fibres 

 terminating in the skin, and which are affected when the 

 skin is touched. The descending motive influence passes 

 from the cord through the anterior roots of the spinal 

 nerves, which ramify and terminate in the muscles where 

 they produce motion. 



It is not, however, necessary that such influence 

 should actually ascend to, or descend from, the brain in 

 order that responsive motions should take place, although 

 it is certain (from observations made on accidentally 

 injured men and purposely mutilated animals) that the 

 brain must act in order to give rise to sensation. 



p 



