CLASS III. 1. 1, OF VOLITION. 275 



CLASS III. 



DISEASES OF VOLITION. 



ORDO I. 



Increafed Volition, 

 GENUS I. 



Increafed Aftions of the Mufcles. 



WE now ftep forward to confider the difeafes of volition, 

 that fuperior faculty of the fenforium, which gives us the pow- 

 er of reafon, and by its facility of action diftinguiflies mankind 

 from brute animals ; which has effected all that is great in the 

 world, and fuperimpofed the works of art on the fituations of 

 nature. 



Pain is introduced into the fyftem either by excefs or defecl: 

 of the action of the part. (Seel:. IV. 5.) Both which circum- 

 ftances feem to originate from the accumulation of fenforial 

 power in the affected organ. Thus when the (kin is expofed to 

 great cold, the activity 04 the cutaneous veflels is diminifhed, and 

 in confequence an accumulation of fenforial power obtains in 

 them, becaufe they are ufually excited into inceilant motion by 

 the ftimulus of heat, as explained in Seel:. XII. 5. 2. Contra- 

 rywife, when the veflels of the fldn are expofed to great heat, 

 an excefs of fenforial power is alfo produced in them, which is 

 derived thither by the increafe of ftimulus above what is natural. 



This accounts for the relief which is received in all kinds of 

 pain by any violent exertions of our mufcles or organs of fenfe ; 

 which may thus be in part afcribed to the exhauftion of the fen- 

 forial power by fuch exertions. But this relief is in many cafes 

 fo inftantaneous, that it feems neverthelefs probable, that it is 

 alfo in part owing to the different manner of progreffion of the 

 two fenforial powers of fenfation and volition j one of them com- 

 mencing at fome extremity of the fenforium, and being propa- 

 gated towards the central parts of it ; and the other commenc- 

 ing in the central parts of the fenforium, and being propagated 

 towards the extremities of it ; as mentioned in Seel. XL 2. i. 



Thefe violent voluntary exertions of our mufcles or ideas to, 

 relieve the fenfation of pain conftitute convulfions and madnefs ; 

 and are diitinguifhed from the mufcular aclions owing to in- 

 creafcd fenfation, as in freezing, or coughing, or parturition, or 



ejedlio 



