210 Philosoph\joJiheIIu77ianMincl [Chap. XIL 



cognisable by our senses, except in its effects. He 

 supposes that the o.vygen which enters into com- 

 bination with the blood in respiration, affords the 

 material for the production of sensorial power; 

 that this fluid is liable to be accumulated or dimi- 

 nished by various circumstances ; that it is con- 

 stantly expended by stimuli, and is probably too 

 fme to be long retained in the nerves^ after its pro- 

 duction in the brain; and, finally, that it is capa- 

 ble of assuming the property of solidity^ or divest- 

 ing itself of this property at pleasure. 



This spirit of animation, or sensorial power, ac- 

 cording to the theory under review, produces con- 

 tractions or motions in the animal fibre, and these 

 iibrous motions/ thus occasioned, are the immedi- 

 ate cause of all our ideas ; an idea being defined 

 " a contraction, or motion, or configuration, of 

 the immediate organs of sense." This spirit has 

 four different modes of action ; or, in other words, 

 the mind possessesybz^r different faculties, which 

 are occasionally exerted, and cause all the con- 

 tractions of the fibrous parts of the body\ These 

 are, 1. The faculty of causing fibrous contractions 

 in consequence of the irritations excited by exter- 

 nal bodies, 2. The faculty of causing contrac- 

 tions in consequence of the sensatioi^ of pleasure 

 or pain. 3. The faculty of causing contractions 

 in consequence of "volition, 4. The faculty of 

 causing contractions in consequence of the asso- 

 ciations of fibrous contractions with other fibrous 

 contractions, which precede or accompany them. 

 These four faculties, during their inactive state, 

 arc termed irritability^ sensibility, voluntarity, and 



