272 Medicine. 



During' the application of any of the above- 

 mentioned stimuli, tlie sensorrai power becomes 

 exhausted; on the contrary, while any of them are 

 withdrawn, it becomes accumulated. 



In order to illustrate and establish his important 

 doctrine of association, Dr. Darwin asserts that 

 there are various circles of associate motions in the 

 animal system, wdiich may take their names from 

 that faculty of the sensorial pov/er by which they 

 are introduced. Those circles, for example, w^hich 

 are introduced by an irritative motion, may be 

 termed irritative associate motions; and, in like 

 manner, the sensitive and voluntary associate mo- 

 tions are produced and denominated. All these 

 several circles of motions act on one another by 

 means of the sensorial power of association; they 

 may be affected by other sensorial motions, such 

 as those of irritation, sensation and volition; and 

 they may be considered as compounded, each one 

 of smaller circles; as for instance, the great circle 

 of irritative associate motions may be supposed to 

 be made up of smaller circles of the same kind. 



Conformably to this scheme of association, the 

 introductory link of any circle of associate motions 

 may have its action increased, diminished, or sus- 

 tained in the natural degree. The first may take 

 place either in consequence of excess of sensorial 

 power, the stimuli being in their accustomed de- 

 gree; or in consequence of excess of stimuli, the 

 sensorial power being in its natural degree; or irl 

 consequence of excess of both. The second may 

 arise either from want of sensorial power, the 

 stimulus being in its usual degree; or, from sub- 

 duction of stimuli, the sensorial power being in its 

 natural quantity; or from want of sensorial powet 

 and subduction of stimuli. The third takes place, 

 when both the sensorial power and the stimuli are 

 in proper degree. In some cases, the morbidlv in- 



