CHAPTER XVIII 

 THE INTELLIGENCE SERVICE 



NERVE CELLS 



" The messengers that preser\ed a communication between the soul and the 

 outward members." Berkeley. 



It is obvious that in an organised conglomeration of cell bodies like 

 the animal body some means of rapid communication must exist 

 between one organ and another. Without it, rapid co-ordinated 

 movement by the body as a whole would be impossible. This 

 work is accomplished by the nervous system. Two entirely 

 different systems of rapid communication exist in the body. One 

 runs to and from the body wall and has to do with the relation 

 of the body to its environment. It belongs to the army of defence 

 and defiance. The other system of rapid communication conveys 

 messages to and from the industrial communities. 



Embryologically, communication between an inland cell and 

 the outer world is effected, in the first instance, by an ingrowth 

 of the external epithelial covering. That is, messages are passed 

 on to the inmost cell by a file of cells, detailed for this service. 

 These cells are, to begin with, all structurally and functionally 

 alike (neuroblasts). Later, some few of them send out long 

 processes towards the surface and towards the organ. These 

 processes end in branching twig-like structures called dendrites 

 (Gr., a tree), through which they seem to be able to pass on 

 stimuli to one another. The name synapse (Gr., a junction), is 

 given to the juxtaposition of the dendrites of a nerve cell or cyton, 

 with the terminal processes of the axon of another cyton. The 

 cell with its processes is called a neuron. (See Fig. 54.) 



The second system of nerves, that of the viscera, is formed of 

 neuroblasts which have migrated towards the organ from the 

 neural canal. They all pass through at least one ganglion or a 

 plexus which acts like a local headquarters or exchange. 



Some nerves have a sheath or coat composed of unsaturated 

 fatty acids and lecithin (and allied lipoids). This medullary 

 sheath is formed from separate cells, but it must retain some 

 connection with the nerve cell, as it dies and disintegrates when 

 dissociated from it, 



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