CH. XLVII*] REFLEX ACTIONS 669 



Reflex Action of the Spinal Cord. 



There are two theories of a speculative nature regarding tho 

 relationship of reflex and voluntary actions : one is, that all actions 

 are in essence reflex, and that the so-called voluntary actions are 

 modified reflexes, in which the afferent impulse to act, though often 

 obscure, is nevertheless, by seeking, always to be found. Put in 

 popular language, this theory implies that we have really no such 

 thing as a will of our own, but our actions are simply the result of 

 external circumstances. 



The other theory is the exact opposite namely, that all actions 

 are in the beginning voluntary, and become reflex by practice in the 

 lifetime of the individual, or the lifetime of his ancestors, who trans- 

 mit this character to their descendants. 



This is not the place to discuss a philosophical question of this 

 kind, and still less the debated question whether acquired characters 

 are transmissible by inheritance. The distinction between voluntary 

 and reflex actions is a useful practical one, and certainly it cannot 

 be doubted that many practised actions become reflex in the lifetime 

 of every one of us. Take walking, skating, or bicycling as examples : 

 at first these acts of locomotion are those in which the brain is con- 

 cerned ; they are actions demanding the concentration of the atten- 

 tion ; but later on the action is largely carried out by the spinal cord, 

 the afferent impulses to the cord from the lower limbs directing the 

 efferent impulses to the muscles concerned. 



The reflex actions of the spinal cord may first be studied in a 

 brainless frog, as in this animal the spinal cord possesses a great 

 power of controlling very complex reflex actions. 



Reflexes in a Brainless Frog. 



After destruction of the cerebrum the shock of the operation 

 renders the animal for a short time motionless and irresponsive to 

 stimuli, but in a few minutes it gradually assumes a position which 

 differs but little from that of a living conscious frog. If thrown into 

 water it will swim ; if placed on a slanting board it will crawl up it 

 (Goltz) ; if stroked on the flanks it will croak (Goltz) ; if it is laid on 

 its back, and a small piece of blotting-paper moistened with acid be 

 placed on the skin, it will generally succeed in kicking it off; if a 

 foot is pinched it will draw the foot away ; if left perfectly quiet it 

 remains motionless. Even when the optic thalami are destroyed 

 also, it still executes complex reflex actions, but all power of balancing 

 and all spontaneity are lost. 



The muscular response that follows an excitation of the surface 

 is purposive and constant, the path along which the impulse is pro- 

 pagated being definite. 



Under certain abnormal conditions, however, the propagation of 



