190 THE HUMAN BODY 



resentative cerebral activity. So far as we can judge it represents 

 in animals the climax of intellectual achievement. No animal 

 has ever been seen to perform any act, not purely reflex, as are all 

 " instinctive " actions, which associative memory cannot account 

 for. The activities of man are for that matter based upon as- 

 sociative memory almost as fully as are those of animals. The 

 important intellectual difference between man and animals is 

 the possession by man of the faculty of reason, which is denied 

 to animals. The power to reason is itself, however, based upon 

 associative memory. It may be roughly explained as the as- 

 sociation of concepts whose relationship is not obvious. An 

 animal, according to this idea, cannot reason because he cannot 

 form associations except of concepts that manifestly belong to- 

 gether. The man reasons by perceiving relationships in appar- 

 ently unrelated facts or ideas. 



We must admit, however, that the most complicated acts of 

 associative memory that have been observed in animals simulate so 

 closely mental processes which in man are ordinarily thought of as 

 reason, that no hard and fast limit of the latter can be set. We 

 would scarcely venture to establish any point as marking the ut- 

 most intellectual achievement in animals, although we would not 

 hesitate to say that in comparison with the possibilities of the 

 human brain the extremest mental process of the most intelligent 

 animal dwindles to insignificance. 



The powers of using language and of reasoning are the only 

 cerebral functions possessed by man and not by animals of which 

 we have positive objective proof. They are therefore the only ones 

 of which physiology can take account at the present time. Physiol- 

 ogy does not thereby deny, however, the existence of many ac- 

 tivities in the human brain which are without counterpart in the 

 brains of lower animals. While associative memory accounts 

 completely for all non-instinctive actions of the lower animals, the 

 history of the human race and the experience of individuals con- 

 tain much that baffles explanation in terms of associative memory 

 or of reason. The factors which lead the race always onward and 

 upward to greater and greater heights of spiritual achievement are 

 beyond the power of present-day physiology to analyze or even 

 discuss. 



Nourishment of the Brain. The cells of the cerebral cortex 



