466 Edward Livingston Youmans. 



the outlook is confident, there is joy in action, and 

 courage in enterprise; but with a low or disturbed cir- 

 culation, thin, morbid blood, and bodily exhaustion, there 

 is depression of spirits, gloom, inaction, paralysis of will, 

 and weariness of life. That variability of mental state 

 which is so striking and general an experience with the 

 literary and artistic classes, the periods when work is im- 

 possible, the moods of sluggish and unsatisfactory effort, 

 the seasons of steady and successful accomplishment, and 

 the moments of rare exaltation, capricious as they may 

 seem, are but the exponents of varying constitutional con- 

 ditions. 



But the part played by the organism becomes still more 

 apparent when we consider the mode of action of the 

 nervous system in producing mental effects. It has been 

 stated that this system is composed of fibres and cells ; 

 hence the simplest conceivable case of nervous activity is 

 where a cell and fibre become active, producing an excite- 

 ment and a discharge, the highest action of the organ 

 being nothing more than a complex system of excitements 

 and discharges. In sleep, for example, a fly lights upon 

 the face, producing an impression, or change, which causes 

 a discharge along the nerves to the grey matter of the 

 spinal cord. Here force is again liberated, which is dis- 

 charged along another set of nerves upon the appropriate 

 muscles, which, being contracted, bring the hand to the 

 place where the fly settled. This is the course of power in 

 a simple reflex action. But when the brain is called into 

 conscious exercise in the higher processes of intellection 

 just the same thing occurs. A person may be engaged in 

 tranquil thinking, when one idea leads on to another in a 

 natural train of association that is, where the excitement 

 of one state of consciousness is discharged into another, 

 forming a succession of cerebral changes. In this quiet 

 course of thought, a ludicrous idea or a witty combination 



