XIII 



SENSATION 



Sensation and consciousness — Unconscious and conscious sensa- 

 tion — Sensibility and irritability — -Reflex sensation and 

 perception of stimuli — Sensation and living force — Re- 

 action to stimuli — Resolution of stimuli — External and 

 internal stimuli — Conveyance of stimuli — Sensation and 

 striving — Sensation and feeling — Inorganic and organic 

 sensation — Light sensation, phototaxis, sight — Sensation 

 of warmth, thermotaxis — Sensation of matter, chemotaxis 

 — Taste and smell — Erotic chemicotropism — Organic sen- 

 sations — Sensation of pressure — Geotaxis — Sensation of 

 sound — Electric sensation. 



SENSATION is one of those general terms that have 

 at all times been liable to the most varied inter- 

 pretations. Like the cognate idea of the "soul," it is 

 still extremely ambiguous. During the eighteenth cen- 

 tury it was generally believed that the function of 

 sensation was peculiar to animals, and was not present 

 in plants. This opinion found its most important ex- 

 pression in the well-known principle in Linn6's Systema 

 NaturcB: "Stones grow: plants grow and live: animals 

 grow, live, and feel." Albrecht Haller, who gathered 

 up all the knowledge of his time relating to organic life 

 in his Elementa PhysiologicB (1766), distinguished as its 

 two chief characters "sensibility" and "irritability." 

 The one he ascribed exclusively to the nerves, and the 

 other to the muscles. This erroneous idea was sub- 

 sequently refuted, and in our own time irritability is 

 conceived to be a general property of all living matter. 



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