Class III. 1. 1. OF VOLITION. 275 



CLASS III. 



DISEASES OF VOLITION. 



ORDO I. 



Increafed Volition, 

 GENUS I. 



Increafed Afiions 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 diftinguifhes 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 defect 

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

 ftances feem to originate from the accumulation of fenforial 

 power in the affected organ. Thus when the Ikin is expofed to- 

 great cold, the activity of the cutaneous veffels is diminished, and 

 in confequence an accumulation of fenforial power obtains in 

 them, becaufe they are ufually excited into inceffant motion by 

 the ftimulus of heat, as explained in 3ect. XII. 5. 2. Contra- 

 rywife, when the veffels of the Ikin are expofed to great heat, 

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

 derived thither by the increafe of stimulus 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 pan 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 cvving to the different manner of progreflion of the 

 two fenforial powers of fenfation and volition ; 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 Sect. XI. 2. 1. 



Thefe violent voluntary exertions of our mufcles or ideas to 

 relieve the fenfation of pain conftitute convulfions and madnefs ; 

 and are didinguifhed from the mufcular actions owing to in- 

 creafed fenfation, as in fneezing, or coughing, or parturition, or 



ejectio 



