NERVOUS INTEGRATIONS IN MAN 249 



Speed of communication and of reaction of one part of 

 the body to happenings at another seems to be part of the 

 "purpose" of this Hving telephone system. Although its 

 microscopic structure and its elemental unit reactions 

 exhibit an almost monotonous uniformity and process, the 

 results which are their outcome are strikingly various and 

 bear, as do so many of the body's reactions (but these even 

 more obviously than most) the feature of "purpose." 

 Thus, by their means a speck of dust in the eye sends 

 messages thence far and wide over the body, all of them 

 conducive to an obvious purpose. Its messages evoke (i) 

 protective movement of the eyelids, (2) protective secretion 

 of tears, (3) protective coming of the hand to the assistance 

 of the eye and indeed a whole train of motor acts toward 

 relief of the situation. Finally (4) that situation is reinforced 

 and therefore protectively accentuated, until relief has 

 come, by superadded mental experience, i.e., pain; the pain 

 we note is hkewise and nr less than the rest of the train 

 of reactions a sequel to, a product and accompaniment of, 

 the neural reaction, mysterious though the relation between 

 it and the material processes still remains. 



The nervous system throughout the whole great class of 

 animals known as vertebrate exhibits the same broad plan of 

 construction, the same character of unit cells or neurones 

 arranged in chains and with conductive thread-like fibers, 

 and the same fundamental reactions, namely impulse 

 conduction and the two opposed processes of excitation and 

 inhibition. In man it does not depart from that plan or 

 from those characters but merely offers the highest and 

 most complex example of them. 



It was said above that a main function of the nervous 

 system is to enable quick appropriate reaction, by movement 

 for the most part, to environmental events significant for 

 the organism, for example escape from being made a prey, or 

 the securing of prey or other food. The primitive nervous 

 system of the more primitive vertebrates secures this end, 

 within usually a more restricted range of circumstances than 

 in the higher vertebrates, and so far as we can Judge by 

 little else than pure reflex action. 



