(II. TV.] SUBSTITUTION OF NERVE- ACTIONS. 283 



yawning, crying, singing, striking, swimming, spinning, building, 



&c. (284), have, as their inducements, various external sensations, 



imaginations, foreseeings, and other instincts ; and it is an esta- 



)lished fact in the whole animal kingdom, that all the actions 



these instinct for voluntary movements may be produced by 



le vis nervosa only. Various experiments and observations 



lade on decapitated frogs and other animals already detailed, 



rove this amply. An acephalous child retracts its limbs when 



winched or burnt, exactly as an ordinary child would have done. 



[t is related, that a decapitated man, being thrust through the 



)reast with a sword, threw his arms together, — a movement 



^bich under ordinary circumstances would have been the sen- 



ient action of the instinct of self-preservation. The movements 



ide by a decapitated man, immediately after decapitation, are 



Tor the most part volitional in character. He struggles violently 



dth his arms, that he may free bis hands from their bonds, and 



10 be able to use them to save himself. He grasps with his 



lands, and endeavours to turn, to stand on his feet, &c. 



Jimilar movements in great variety may be seen daily in 



lecapitated animals, as turtles, snakes, snails, flies, centipeds, 



:c. Many of this class of movements, as singing, sighing, &c., 



jannot, however, be excited as nerve-actions, because decapita- 



ion renders the experiment impossible, the organs themselves 



)eing removed. 



556. From the preceding and other considerations already 



idduced (435 — 439), it is extremely probable, that these actions 



)f the instincts, ordinarily voluntary movements in all animals 



'^hich feel true instincts, often take place as pure nerve- 



|actions (269); that they are sometimes of the one kind, some- 



Itimes of the other (286) ; and, consequently, that animals which 



[are endowed with neither sensation nor true instincts, being 



Simulated solely by unfelt external impressions, can apparently 



[act volitionally, and as if endowed with sensation. Respiration 



pas already been quoted as an example of this kind (285, 526). 



iWhen the instinct of an animal excites it to walk or run 



[Toluntarily in a certain locality, the muscles of the legs 



[are only sentiently excited at first to the suitable movements, 



id, subsequently, an external impression is sufiicient to 



^excite the same movements. Thus there are examples of 



^persons who continually traverse the same streets, who fall fast 



