THE STORY OF THE BRAIN AND NERVE 109 



higher animals thus become raised from the auto- 

 matic or machine-like life of their lower kith and kin, 

 and develop accordingly degrees of intelligence and 

 independent action, which vary with their rank ; this 

 advance attaining naturally its highest development 

 in man and his neighbour animals. In the human 

 domain we meet a still further development of the 

 work of the nervous system. In addition to the regu- 

 lated play of instinct, a higher intelligence appears 

 as well, to which we apply the terms reason and 

 consciousness. It may be said that the highest level 

 of nervous work is found in the case of man, 

 because he is conscious not merely of his own 

 existence, but is also enabled to reason out and 

 to understand generally the conditions under which 

 that existence is passed, whilst he is also enabled 

 to adapt his life much more readily than his 

 animal neighbours to the varying conditions of 

 life. Having regard to the fact that nerve cells, 

 or, in the case under discussion, brain cells, represent 

 the highest items in man's bodily structure, the 

 question naturally arises whether science can lead 

 us to a perfect understanding of the manner in 

 which these cells govern and control existence. 

 This much is certain, at least, that the living matter 

 of the brain cells is the seat of those particular 

 changes and actions arising from the play of nerve 

 force, which can be converted into force or energy 

 of other kinds. Thus a thought arising in, or 

 produced by, certain brain cells can be converted at 

 once into movements either simple or complex. The 

 act of writing or of speaking, for example, involves 

 a whole series of brain actions, the main feature of 

 which is the conversion of thought which need not 

 necessarily manifest itself externally at all into a 



