THE STORY OF THE BRAIN AND NERVE 105 



marvellously short of human acquirements, even in 

 respect of those traits which mark a simple mental 

 or nervous operation on the part of man. The dog, 

 in other words, cannot relate itself in such a clear 

 and perfect manner to the world in which it lives as 

 does the man, and the human superiority arises 

 undoubtedly from that higher evolution and develop- 

 ment of his nervous apparatus which marks the 

 human estate. 



THE ESSENTIALS OF A NERVOUS SYSTEM. If we 

 compare the nervous system to that of a telegraph, 

 we may find the comparison to be thoroughly justified. 

 In the construction of the ordinary telegraph system 

 two chief elements have to be provided. We have 

 first to supply batteries or means for developing 

 electrical energy, and wires require to be furnished 

 for the purpose of carrying or conducting the 

 electrical force. Even if wireless telegraphy be 

 included in such a comparison, the electrical waves 

 will require conduction. The nervous system, 

 following out this comparison, complicated as it may 

 be, is built up of two elements which roughly 

 correspond to those of the telegraph apparatus. 

 These two elements are first, nerve cells, and second, 

 nerve fibres. It is important to distinguish between 

 the functions of these two elements. Their uses are 

 as clearly defined and distinct as are the batteries and 

 wires of the telegraph. Nerve cells are the origina- 

 tors and receivers of the messages or impressions 

 through which the nervous system is stimulated to 

 its work. A nerve fibre on the other hand, is a mere 

 conductor or conveyer of such messages. A nerve 

 has no power of initiating any message on its own 

 account. In order that a nerve fibre may be stimulated 

 to carry a message, either from brain to body or 



