22i TRANSFORMATION AND EQUIVALENCE OF FORCES. 



with the supply of blood to the brain. On the one hand, a 

 cessation of the cerebral circulation, from arrest of the 

 heart's action, immediately entails unconsciousness. On the 

 other hand, excess of cerebral circulation (unless it is such 

 as to cause undue pressure) results in an excitement rising 

 finally to delirium. Xot the quantity only, but 



also the condition of the blood passing through the nervous 

 system, influences the mental manifestations. The arterial 

 currents must be duly aerated, to produce the normal 

 amount of cerebration. At the one extreme, we find that if 

 the blood is not allowed to exchange its carbonic acid for 

 oxygen, there results asphyxia, with its accompanying stop- 

 page of ideas and feelings. While at the other extreme, we 

 find that by the inspiration of nitrous oxide, there is pro- 

 duced an excessive, and indeed irrepressible, nervous ac- 

 tivity. Besides the connexion between the develop- 

 ment of the mental forces and the presence of sufficient 

 oxygen in the cerebral arteries, there is a kindred connexion 

 between the development of the mental forces and the pres- 

 ence in the cerebral arteries of certain other elements. 

 There must be supplied special materials for the nutrition of 

 the nervous centres, as well as for their oxidation. And 

 how what we may call the quantity of consciousness, is, other 

 things equal, determined by the constituents of the blood, is 

 unmistakeably seen in the exaltation that follows when cer- 

 tain chemical compounds, as alcohol and the vegeto-alkalies, 

 are added to it. The gentle exhilaration which tea and 

 coffee create, is familiar to all; and though the gorgeous 

 imaginations and intense feelings of happiness produced by 

 opium and hashish, have been experienced by few, (in this 

 country at least,) the testimony of those who have experi- 

 enced them is sufficiently conclusive. Yet another 

 proof that the genesis of the mental energies is immediately 

 dependent on chemical change, is afforded by the fact, that 

 the effete products separated from the blood by the kid- 

 neys, vary in character with the amount of cerebral action. 



