THE NEKVOUS SYSTEM 



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functions, so far as we have considered them hitherto, are 

 automatic, from a mechanician's point of view. Their situa- 

 tion and connections determine the direction in which they 

 conduct, and the degree in which they reinforce stimuli im- 

 pressed upon the nervous system by the environment, including 

 what may be termed the internal environment, food in the 

 alimentary canal, secretions in ducts, and so forth. Have the 



FIG. 22. THE BODY OF A MOTOR NEURONE. 



In its centre is a large clear spherical nucleus, with a nucleolus. The body-substance is pro- 

 longed into five dendrites and an axon. Neuro-nbrillse are seen in dendrites and axon. 

 They traverse the body of the cell in all directions, in little bundles which are separated by 

 angular granules of stainable substance (tigroids). 



cells any directive or executive functions ? There is no 

 evidence that they have ; nor, it must be added, is there any 

 line of reasoning which leads inevitably to the conclusion that 

 they have not. Remembering that, until recently, it was the 

 custom to solve all obscure problems and to shelve all diffi- 

 culties by conferring human attributes upon nerve-cells and 

 collections of nerve-cells, termed " centres," a physiologist 

 admits the negative with reluctance. The unconscious argu- 



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