476 Edward Livingston Youmans. 



Thus viewed, every attainment involves the exercise of 

 brain power each acquisition is a modification of cerebral 

 structure. All sensations of objects and words that we 

 remember, all acquired aptitudes of movement ; the asso- 

 ciations of the perception of things with visible symbols, 

 vocal actions and sounds, the connection of ideas with feel- 

 ings and emotions, and the formation of intellectual and 

 moral habits, are all concomitants and consequents of the 

 only kind of action of which the brain is capable are all 

 the products of organic nutrition ; and the rate and limit 

 of acquisition, as well as the capacity for retention, are 

 conditioned upon the completeness of the nutritive pro- 

 cesses. As each acquirement involves a growth it is 

 evident that acquisition may reach a point at which the 

 whole organic force is consumed in conserving it, and 

 further attainments can only be made at the expense of 

 the decay and loss of old ones. Hence, if we overburden 

 the brain, as in school " cramming," nutrition is imperfect, 

 adhesion feeble, and acquisition quickly lost. 



The one great physiological law upon which bodily and 

 mental health are alike dependent is the alternation of 

 action and repose which results from the limitation of 

 power. The eternal equation of vital vigour is, rest equals 

 exercise. That tendency to rhythmic action, which seems 

 to mark all displays of power in the universe, is con- 

 spicuously manifested in the organic economy, allowing 

 the muscles of respiration eight hours' repose out of 

 twenty-four, and six hours' rest to those of the heart. 

 The cerebral rhythm is diurnal ; except that rest which 

 parts of the brain may obtain when only other parts are 

 in action, the organ finds its appropriate repose in sleep. 

 " Half our days we spend in the shadow of the earth, and 

 the brother of death extracteth a third part of our lives," 

 says the eloquent Sir Thomas Browne ; that is, the perio- 

 dicities of cerebral action are defined by astronomic cycles ; 



