122 PHYSICAL BASIS OF THOUGHT. 



to explain the operation clearly, adequately, and conclu- 

 sively. We have, it is said, a plastic substance, a sort of 

 clay, capable of molecular change, which is the physical 

 basis of thought, of consciousness, and even of morals ! 



But whatever opinion may be speculatively entertained 

 upon such a question, all must acknowledge that nothing 

 exact is known concerning the different phenomena which 

 take place in the matter of the brain when the operation of 

 thinking is proceeding actively and when it is suspended. 

 Besides this, it must be borne in mind fnat there are 

 brains that think and brains that have not the power of 

 thinking. Between these two classes of brains there must 

 be essential differences as regards the structure of the 

 cerebral tissue and the arrangement of its anatomical 

 elements. And yet no one has succeeded in demonstrating 

 the striking and essential differences that all admit must 

 undoubtedly exist. Nor could any one premise from the 

 most minute examination of the texture of a human brain 

 that it was taken from a thinking apparatus, any more than 

 he could feel sure from its structural character, that the 

 brain of a sheep was a nervous mechanism incapable of 

 manifesting reason or morals. How, therefore, is it pos- 

 sible that a question of such advanced physiology as the 

 one alluded to can be looked upon as determined at this 

 time ? Here, as in many other cases, dogmatic assertions 

 on the part of some who are invested with authority, are 

 accepted and taught as if they were scientific inferences 

 based upon facts of observation and experiment, and capable 

 of proof. 



The nature, composition, mode of action, nay, even the 

 origin of man, are treated of in many modern books as if 



