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 Linnd's System a 

 Natiircu: "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 Elemcnta Physiologic^ (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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