THE SPINAL CORD. 405 



The neck had been severed, in the above case, near the level of the 

 fourth cervical vertebra. 



Reflex action may also be seen, in man, in certain cases of disease 

 of the spinal cord. If the upper portion of the cord be disintegrated 

 by inflammatory softening, so that its middle and lower portions lose 

 their connection with the brain, paralysis and insensibility ensue in 

 all parts below the seat of the lesion. Under these conditions, the 

 patient is incapable of voluntary motion in the paralyzed parts, and 

 is unconscious of any injury to the integument in the same region. 

 But if the soles of the feet be gently irritated with a feather or with 

 the point of a needle, a convulsive twitching of the toes will often 

 take place, or even retractile movements of the leg and thigh ; and 

 such movements may frequently be excited by the sudden contact of 

 cool air with the lower limbs. We have repeatedly witnessed these 

 phenomena, in disease of the spinal cord, where the paralysis and 

 insensibility of the lower limbs were complete. Many similar instances 

 have been reported by various authors. 



Physiological Action of the Spinal Cord as a Nervous Centre. The 

 reflex action of the spinal cord, as it takes place in the healthy condi- 

 tion, is not easily brought under observation. In animals, unless the 

 head be removed or the spinal cord separated from the brain, reflex and 

 voluntary movements are liable to be confounded ; and in man during 

 health, the phenomena of sensation and volition are so prominent as 

 to obscure those which are independent of the will. Nevertheless, the 

 latter are exceedingly important, and many of them in almost constant 

 operation. 



The general character of reflex actions of the spinal cord is that 

 they tend unconsciously to the defence or preservation of the body. 

 This is seen in the simplest experiments on animals. If a decapitated 

 frog be suspended in the air, the posterior limbs hang downward 

 in a perfectly relaxed condition. On pinching one of the feet, or 

 immersing it in acidulated water, the limb is retracted by its flexor 

 muscles, the result being a withdrawal of the foot. The muscles 

 then relax, and the limb lengthens until the foot touches the irritating 

 liquid, when it is again drawn up ; and so on, until the irritability of 

 the cord is so far diminished that it no longer reacts. In this case, 

 therefore, the only muscles thrown into activity are the flexors, which 

 tend to withdraw the foot from the source of irritation. When an 

 irritation is applied to the side of the trunk, it is common to see a 

 hind foot brought to the irritated spot, as if to protect it ; and in some 

 instances the adaptation of reflex movements to accomplish a definite 

 result is very marked. This cannot be attributed to any faculty of 

 perception in the spinal cord ; since we know, from pathological cases 

 in man, that when the cord is separated from the brain by disease or 

 injury, the parts below are absolutely deprived of sensibility and voli- 

 tion. The movement produced therefore depends simply on the struct- 

 ure of the limbs and the nervous mechanism of the spinal cord. In 



