186 



Dr. H. Head. 



Secondly, some reaction, normally dominated or suppressed, may break 

 through owing either to the extreme vehemence of the stimulus or to 

 diminution of the controlling energy, due to causes other than organic 

 destruction. Here the whole of the morbid manifestations consist of positive 

 signs and symptoms imaccompanied by loss of function. This I shall call 

 " escape from control." 



1. Disintegration. 



Sherrington's physiological work on the reflexes [16], and especially his 

 explanation of decerebrate rigidity, gave an experimental proof of Jackson's 

 law of release of function. If the cerebral hemispheres are removed, or better 

 still, if the animal is decapitated through the mid-brain, all four limbs fall into 

 a condition of postural rigidity, due to prolonged spasm of certain voluntary 

 muscles. The head is lifted and the tail may be stiffly curved upwards. 

 This attitude is essentially adapted to resist the force of gravity and, if the 

 limbs are passively flexed by the experimenter, considerable resistance is 

 encountered. The knee-jerk assumes a characteristic form ; on tapping the 

 tendon a quick extensor movement is produced, but the limb does not return 

 to its original position. Kemoval of controlling influences from above 

 permits these postural activities of lower centres to manifest themselves 

 unchecked, for the cortex is concerned mainly with the initiation or inhibition 

 or movement and not with posture. 



When the spinal cord is divided in man, or so gravely injured that conduc- 

 tion is destroyed, the lower extremities lie flaccid and atonic on the bed, in 

 any position into which they may be placed. The urine is retained and the 

 patient has no power of evacuating his bowels. All deep reflexes are 

 abolished, and scratching the sole of the foot may either produce no move- 

 ment of the toes or one that is feebly downwards ; the receptive field for this 

 reflex is restricted to the sole or even to the outer portion of the under 

 surface of the foot. 



Should the patient be young and strong, particularly if he remains free 

 from cystitis, bed-sores, or fever, the deep reflexes reappear as the period 

 of spinal shock passes away. The ankle jerk and then the knee jerk can be 

 obtained ; gradually the plantar reflex begins to assume a form characterised 

 by an upward movement of the great toe. The field from which it can be 

 evoked enlarges, and finally, in successful cases, the spinal cord becomes 

 so excitable that stimulation anywhere below the level of the lesion may 

 be followed by a characteristic upward movement of the toes. But this is 

 a small portion only of the movements produced by nocuous stimulation ; 

 the ankle is dorsiflexed and the lower extremity bent both at knee and 

 hip ; not infrequently the abdominal wall contracts and every flexor muscle 



