INTRODUCTION TO NEUROLOGY 



CHAPTER I 



BIOLOGICAL INTRODUCTION 



THE living body is a little world set in the midst of a larger 

 world. It leads in no sense an independent life, but its con- 

 tinued welfare is conditioned upon a nicely balanced adjust- 

 ment between its own inner activities and those of surrounding 

 nature, some of which are beneficial and some harmful. The 

 great problem of neurology is the determination of the exact 

 part which the nervous system plays in this adjustment. 



This problem is by no means simple. The search for its 

 solution will lead us, in the first place, back to an examination 

 of some of the fundamental properties of the simplest living 

 substance, of protoplasm itself; and in the last analysis it will 

 involve a consideration of the highest mental capacities of the 

 human race and of the physiological apparatus through which 

 these capacities come to expression. We shall first take up the 

 nature of this adjustment on the lower biological levels. 



All of the infinitely diverse forms of living things have cer- 

 tain points in common, so that one rarely has any doubt 

 whether a given object is alive or dead. Nevertheless, the 

 precise definition of life itself proves very difficult. Herbert 

 Spencer, in his "Principles of Biology," after many pages 

 of close argument and rather formidable verbal gymnastics, 

 arrived at this formula: Life is "the definite combination of 

 heterogeneous changes, both simultaneous and successive, in 

 correspondence with external coexistences and sequences"; 

 or, more briefly, "The continuous adjustment of internal re- 

 lations to external relations." A somewhat similar idea was 



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