

ACTION AS A NERVOUS CENTRE. 463 



afterward the scratching of the skin over the chest produced only con- 

 tractions in the great pectoral muscle which hardly stirred the arm." 



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

 the fourth cervical vertebra. 



The reflex action may also be seen very distinctly in the human sub- 

 ject, 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 natural connection with the brain, 

 paralysis of voluntary motion and loss of sensation ensue in all parts 

 of the body below the seat of the anatomical lesion. Under these con- 

 ditions, the patient is incapable of making any muscular exertion in the 

 paralyzed parts, and is unconscious of any injury done to the integu- 

 ment 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, and even retractile movements of the leg 

 and thigh, altogether without the patient's knowledge. Such move- 

 ments may frequently be excited by simply allowing the cool air to 

 come suddenly in contact with the lower extremities. We have 

 repeatedly witnessed these phenomena, in a case of disease of the spinal 

 cord, where the paralysis and insensibility of the lower extremities 

 were complete. Many similar instances have been reported by various 

 authors. 



Physiological Action of the Spinal Cord, as a Nervous Centre, during 

 health. The physiological character of the reflex action of the spinal 

 cord, as it takes place in the healthy condition, is not easily brought 

 under observation. In animals, unless the head be removed or the 

 spinal cord separated from the brain, the reflex and voluntary move- 

 ments are liable to be confounded ; and in man during health the phe- 

 nomena of sensation and volition are so prominent, as to conceal or 

 obscure those which are performed independently of the consciousness 

 and the will. Nevertheless, the latter are exceedingly important, and 

 many of them in almost constant operation. 



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

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

 This character is even seen in the simple experiments performed upon 

 the decapitated frog. If the frog in this condition be suspended in the 

 air by its anterior extremity, the posterior limbs hang downward in a 

 perfectly relaxed condition. On pinching the integument of a foot, or 

 immersing it in acidulated water, the limb is drawn upward by contrac- 

 tion of its flexor muscles, and the result of this movement is a with- 

 drawal of the foot from the source of irritation. When the muscles 

 relax, the limb lengthens until the foot again touches the irritating 

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

 the cord is so far diminished, or accustomed to that particular stimulus, 

 that it no longer reacts. In this case, therefore, it is not all the mus- 

 cles of the leg and thigh which are thrown into activity by irritating 

 the skin, but only the flexors, which tend to withdraw the foot from the 



