COEEELATION OF PHYYSICAL AND MENTAL FOKCES. XXXV 



attachments than the latter, whose unexpended emotions become 

 permanent elements of character. Tor the same reason, those who 

 are loud and vehement in their lamentations seldom die of grief; 

 while the deep-seated emotions of sorrow which others cannot 

 work off in violent demonstrations, depress the organic functions, 

 and often wear out the life. 



The intellectual operations are also directly correlated with 

 physical activities. As in the inorganic world we know nothing 

 of forces except as exhibited by matter, so in the higher intellectual 

 realm we know nothing of mind-force except through its material 

 manifestations. Mental operations are dependent upon material 

 changes in the nervous system ; and it may now be regarded as a 

 fundamental physiological principle, that " no idea or feeling can 

 arise, save as the result of some physical force expended in pro- 

 ducing it." The directness of this dependence is proved by the 

 fact that any disturbance of the train of cerebral transformations 

 disturbs mentality, while their arrest destroys it. And here, also, 

 the correlation is quantitative. Other things being equal there is a 

 relation between the size of the nerve apparatus and the amount 

 of mental action of which it is capable. Again, it is dependent 

 upon the vigor of the circulation ; if this is arrested by the cessation 

 of the heart's action, total unconsciousness results; if it is enfeebled, 

 mental action is low ; while if it is quickened, mentality rises, even 

 to delirium, when the cerebral activity becomes excessive. Again, 

 the rate of brain activity is dependent upon the special chemical 

 ingredients of the blood, oxygen and carbon. Increase of oxygen 

 augments cerebral action, while increase of carbonic acid depresses 

 it. The degree of mentality is also dependent upon the phosphatic 

 constituents of the nervous system. The proportion of phosphorus 

 in the brain is smallest in infancy, idiocy, and old age, and greatest 

 during the prime of life ; while the quantity of alkaline phosphates 

 excreted by the kidneys rises and falls with the variations of mental 

 activity. The equivalence of physical agencies and mental effects 

 is still further seen in the action of various substances, as alcohol, 



