268 Medicine. 



probable the improvements of future times will 

 serve much further to elucidate and confirm. 



Brown assumed, as the foundation of his system, 

 the existence of an unknown principle, on which, 

 when acted upon by stimuli, all the phenomena of 

 life, health and disease depend, and which he de- 

 nominated excitability. This excitability lie be- 

 lieved to vary in different animals, and in the same 

 animal at different times. As it is more intense, 

 the animal is more susceptible of the action of ex- 

 citing powers. Exciting powers, or stimuli, may 

 be referred to two classes ; either external, as heat, 

 food, wine, poisons, contagions, the blood, se- 

 creted fluids and air; or internal, such as the func- 

 tions of the body itself, muscular motion, thought, 

 emotion and passion. Excitability produces no 

 effect, or rather does not exist, unless exciting 

 powers are applied; for if they are entirely with- 

 drawn, death as certainly ensues as when excita- 

 bility is consumed by the excessive application of 

 them; \\{Q\^\\\Qx<ciQ>x^?L forced state. Excitement 

 may be, in just measure, too great or too small. 

 Stimuli applied in due proportion produce that just 

 degree of excitement which constitutes the state 

 of health. If the stimuli are diminished below the 

 healthy proportion, he supposed the excitability 

 to accumulate ; if increased beyond this propor- 

 tion, to be expended; and on these opposite states 

 he attempted to found a theory of diseases, de- 

 nominating the former direct,, the latter indirect 

 debility. Diseases he divided into two classes, 

 jSthenic and Asthenic, or such as arise from in- 

 creased or diminished excitement. He believed 

 no agent on the living body could properly receive 

 the title o^ sedative ; and insisted that every povver 

 that acts on such a body is stimulant, or produces 

 excitement by expending excitability. Whatever 

 powers therefore may be employed, and however 



