582 THE HUMAN BODY. 



bility. If a frog's brain be removed and the animal's toe 

 be dipped into very dilute acid, it will be removed after a 

 few seconds; the time elapsing between the immersion and 

 the lifting of the foot is known as the reflex time; any- 

 thing diminishing reflex excitability increases this, as the 

 stimulus (which has a cumulative effect on the centre) has 

 to act longer before it arouses the cord to the discharging 

 point. If the sciatic nerve of the other leg be stimulated 

 while the toe is in the acid the reflex time is increased, or 

 the reflex may fail entirely to appear. This is one case of 

 a general law, that any powerful stimulation of one sen- 

 sory nerve tends to inhibit orderly reflexes due to the ex- 

 citation of another. A common example is the well-known 

 trick of pinching the nose or upper lip to prevent a sneeze. 

 The whole question of reflex inhibition is at present very 

 obscure. It may be due to the excitation of special fibres 

 which inhibit reflex centres, as pneumogastric fibres do the 

 cardio-motor; or to the fact that one nerve impulse in the 

 cord in some cases blocks or interferes with another; or 

 partly to both. 



Psychical Activities of the Cord. SinC__wj3--Gan__gL 

 quite marked reflex movements in the lower part of the 

 Body^ of a man whose cord is divided and whaoiannot 

 voluntarily move his lower limbs, and on questioning him. 

 find that he feels nothing and is quite ignorant of his 

 movements unless he sees his legs, it is most probable that 

 the^s^inal cord in all cases is devoid of centres of conscious^ 

 ness and volition: this is not certain, however; for there 

 might well be a less division of physiological labor between 

 the cord and brain of a frog, than between those of a man. 

 Still we are entitled to good evidence before we admit that 

 things so similar as the human cord and that of the frog pos- 

 sess different properties. Co-ordinated movements follow- 

 inga given stimulus, or cries emitted by an animal, will not 

 suffice to prove that it is conscious, since we know these may 

 occur entirely unconsciously in men, who alone can tell us of 

 their feelings. We must look for something that resembles 

 actions only done by men consciously. In the frog it has 

 been maintained that we have evidence of such. If a bit of 



