The Descent of Man 29 



To avoid ambiguity and obscurity, it may be well here to 

 state plainly certain very elementary matters. The ordinary 

 antecedents and concomitants of distinctly felt sensations 

 may exist, with all their physical consequences, in the total 

 absence of intellectual cognisance, as is shown by the well- 

 known fact, that when through fracture of the spine the lower 

 limbs of a man are utterly deprived of the power of feeling, 

 the foot may nevertheless withdraw itself from tickling just 

 as if a sensation was consciously felt. Amongst lower 

 animals, a decapitated frog will join its hind feet together to 

 push away an irritating object just as an uninjured animal 

 will do. Here we have coadjusted actions resulting from 

 stimuli which normally produce sensation, but occurring 

 under conditions in which cerebral action does not take place. 

 Did it take place, we should have sensations, but by no means 

 necessarily intellectual action. 



' Sensation ' is not ' thought,' and no amount of the former 

 would constitute the most rudimentary condition of the 

 latter, though sensations supply the conditions for the exist- 

 ence of ' thought ' or ' knowledge.' 



Altogether, we may clearly distinguish at least six kinds 

 of action to which the nervous system ministers : — 



I. That in which impressions received, result in appro- 

 priate movements without the intervention of sensation or 

 thought, as in the cases of injury above given. — This is the 

 reflex action of the nervous system. 



II. That in which stimuli from without, result in sensa- 

 tions through the agency of Avhich their due effects are 

 Avrought out. — Sensation. 



III. That in which impressions received, result in sensa- 

 tions, which give rise to the observation of sensible objects. 

 — Sensible perception. 



IV. That in which sensations and perceptions continue to 

 coalesce, agglutinate, and combine in more or less complex 



