142 ANIMAL-SENTIENT FORCES. [i. 



their usual order, and the imperfect expressions of move- 

 ments, which, during the gratification of the instinct, become 

 perfect, are abolished. But inasmuch as the gratification of 

 the instinct is itself a sensation, it also, like a true sensation, 

 develops special sentient actions in the mechanical machines, 

 and these do not belong to the instinct. To this class belong 

 the convulsions that occur during the satisfaction of the instinct 

 of sexual congress, being excited by the excessive titillation. 

 When, as in this case, and in all the true blind instincts, the 

 satisfying sensation is an external sensation, the external 

 impression can excite special nerve-actions in the mechanical 

 machines (183), which are altogether foreign to the instinct, 

 and never belong, as such, to its gratification (184, i). 



276, i. Although strong sensational desires and aversions, 

 may and do frequently occur, which are not induced or satisfied 

 by external sensations, nor require to those ends an external 

 impression, but which are based on imaginations, fictions, 

 visions, appearances, forebodings, &c., and are satisfied by them, 

 yet still they all arise from sensational stimuli, and are indirectly 

 determined, both as to their excitation and satisfaction, by ex- 

 ternal impressions (66). But as regards the regular and truly 

 natural instincts, imparted by the Creator to animals for the 

 conservation of their existence and well-being (262), all, so far as 

 we observe them, are excited and satisfied by external sensations, 

 which require true external impressions (258); these are provided 

 before-hand by nature, and so brought into connection with the 

 whole phenomena of life, that they must aff'ect the animal at 

 the right time and place, at such a period, with such intensity, 

 and in such a way, too, that the instinct is duly excited, and at 

 last satisfied in the way already illustrated (265 — 268). 



ii. Since pleasurable and painful feelings derived from ex- 

 ternal impressions constitute the stronger sensational stimuli 

 (80, 88), such constitute also the most suitable stimuli of the 

 peculiarly natural instincts of animals (262, 90), and nature has, 

 therefore, specially made use of them for the development of 

 the absolutely necessary instincts, so that the latter may be 

 kept in action in animals in the most eff'ectual manner. 



iii. No disagreeable external sensation, and therefore no 

 pain, is ever an object of satisfaction to an instinct, but only 

 the agreeable sensation that is the contrary thereof (262, 80, 81). 



