On the Siicntijii Stithy oj Human Nature. 



of power; power depends upon change, and change 

 upon circulation ; the lungs and heart are therefore immedi- 

 ately involved. To high and sustained mental power, ample 

 luniks and a vigorous heart are essential. And these orj^ 

 again, fall back upon the digestive apparatus, which, if 

 feeble, may impair the capacity of a good heart, sound 

 lungs, and a well-constituted brain. Digestion, and even 

 the caprice of appetite, thus stand in direct dynamic rela- 

 tion to intellectual results. 



As. the brain is more largely dependent than any other 

 organ upon the torrent of blood which pours through it, 

 we find that even a transient variation in the supply dis- 

 turbs the course of thought. If a portion of the skull is 

 removed and pressure be made upon the brain, conscious- 

 ness disappears ; and the same thing occurs in fainting, 

 from suspension of the circulation. With invigorated ac- 

 tion of the heart there is a general exaltation of the men- 

 tal powers, while an enfeebled circulation depresses mental 

 activity. Apoplectic congestion produces stupor and in- 

 sensibility ; inflammation of the grey substance causes de- 

 lirium ; while inflammation of the fibrous portion produces 

 torpor and diminishes the power of the will over the mus- 

 cles. In thus saying that the state of the blood influences 

 the mind, we do not use the term mind in any vague or ab- 

 stract sense ; we mean that it affects our views, opinions, 

 feelings, judgments, actions. Change of circulation alters 

 our mental pitch, and with it our relation to the universe. 

 Dr. Laycock observes : " In the earliest stage of general 

 paralysis there is a feeling of energy. Everything, there- 

 fore, appears hopeful to the patient ; large enterprises, the 

 success of which he never doubts, occupy his mind, and he 

 rushes sometimes into the most extravagant and wasteful 

 speculations. This is the stage of erethism of the capil- 

 laries of the part of the brain affected, when it is just 

 sufficient to excite increased cerebral vigour. If, how- 



