114 HUMAN PHYSIOLOGY 



name motor root, because its nerve fibres are 

 destined to convey messages resulting in movement, 

 is given to the anterior or front root, whilst the 

 posterior is known as the sensory root, such a 

 root being the means for conveying impressions 

 made on the ends of nerves, and proceeding 

 onwards to the spinal cord and brain. It follows 

 that the nerves of sense belonging to eyes, ears, 

 nose, etc., are " sensory " nerves, because they 

 only convey messages in one direction, from body 

 to brain and cord. 



THE SPINAL CORD AS A CENTRE. Having regard 

 to the fact that the spinal cord contains an abundant 

 supply of nerve cells, we may again remind ourselves 

 that it is much more than a collection of nerve 

 fibres, since the possession of cells confers upon it 

 the power of acting as a nerve centre, or rather as a 

 series of nerve centres. There is little doubt that 

 a large number of actions, having reference to bodily 

 movements and other functions, can be carried out 

 by the spinal cord independently of the brain, whilst 

 the cord may also be regarded as acting in harmony 

 with the brain in the performance of many of the 

 acts which characterise our voluntary life. Proof 

 that the spinal cord possesses a certain independent 

 action of the brain, is afforded by an experiment in 

 which a decapitated frog has a drop of vinegar or 

 mustard placed on the web of one of its hind feet. 

 It will use the other foot to wipe off the offending 

 substance, and will execute a variety of complex 

 movements to attain this end. Similarly, in the case 

 of a human being who has suffered an accident 

 resulting in the division of his spinal cord, and is 

 therefore unable to move any part below the break, 

 if the foot be tickled the legs will be drawn up. In 



