The Faculties of the Sensorium. 13 



VIII. These four faculties of the sensorium during their inactive 

 state are tei'ined irritability, sensibility, voluntarily, and associability; 

 in their active state they are termed as above irritation, sensation, 

 volition, association. 



Irritation is an exertion or change of some extreme part of the 

 sensorium residing in the muscles or organs of sense, in consequence 

 of the appulses of external bodies. 



Sensation is an exertion or change of the central parts of the sen- 

 sorium, or of the whole of it, beginning at some of those extreme 

 parts of it, which reside in the muscles or organs of sense. 



Volition is an exertion or change of the central parts of the senso- 

 rium, or of the whole of it, terminating in some of those extreme 

 parts of it, which reside in the muscles or organs of sense. 



Association is an exertion or change of some extreme part of the 

 serrsorium residing in the muscles or organs of sense, in consequence 

 of some antecedent or attendant fibrous contractions; see Zoonomia, 

 Vol. I. 



The word sensorium is used to express not only the medullary 

 part of the brain, spinal marro\r, nerves, organs of sense and muscles, 

 but also at the same time that living principle, or spirit of animation, 

 which resides throughout the body, without being cognizable to our 

 senses except by its effects. 



