v SPINAL CORD AND NERVES 299 



wishes to reach an object with a limb in which only the sensibility 

 of the skin of the hand is preserved, its movement is irregular and 

 zig-zag, and it often grasps objects lying near the thing to which 

 the movement was directed. 



According to H. Munk, who tested these results o'f Sherrington 

 and Mott by experiments on the macaque monkey, on cutting the 

 dorsal roots of one arm the immobility of this limb is not so 

 complete as was asserted by the above authors. It is only the 

 movements normally observed on stimulating the afferent nerves 

 of the limb that disappear ; the other movements seem to be 

 difficult and temporarily or permanently impaired in proportion 

 as the excitability of the central organs from which they are 

 evoked is diminished, owing to the suppression of the excitations 

 that normally reach them by the sensory paths. 



Bickel (1897) observed that the effects of severing the afferent 

 paths in the dog are greatly aggravated by lesions of the labyrinth. 

 A similar effect is also obtained by cutting out the retinal 

 sensations. 



H. E. Bering, Sherrington, and Bickel all agree that mechanisms 

 exist, more particularly in the cerebral hemispheres, which are 

 capable of compensating the loss of afferent control in animals 

 with paralysed sensibility. Bickel and Jacob (1900) saw that 

 the disturbance of gait in dogs that have lost sensibility in the 

 hind-limbs gradually diminishes in time till it disappears. " If 

 after this compensation has been established the senso - motor 

 zones of the cerebral cortex in relation with the hind-limbs are 

 destroyed, the ataxic disturbances reappear, and are again compen- 

 sated slowly and feebly never to the former extent." Merzbacher 

 (1902) found the same on the frog. 



The experiments of Trendelenburg (1906) on pigeons, in which 

 the dorsal roots of various regions of the cord had been cut, agree 

 fundament illy with the above. Bilateral section of the dorsal 

 roots which innervate the wings crippled the animals permanently 

 for flight, while bilateral section of the dorsal roots for the legs 

 caused permanent incapacity for standing. After unilateral section 

 of the same roots a great difference is seen in the behaviour of the 

 wings and the feet, as this operation does not interfere with normal 

 flight, signs of dysmetria being perceptible only in certain reflexes 

 (abnormal lifting of the wing), but unilateral section of the lumbo- 

 sacral roots produces marked ataxia, which at first hinders both 

 standing and walking. The animal only learns to use its limbs 

 again by degrees, the disturbances of innervation, particularly in 

 locomotion, being plainly shown by an abnormal raising of the 

 leg, analogous to the Hebphanomen which Hering described for 

 the frog. The reason for this dissimilar behaviour of the wing 

 and the leg lies in the fact that the wings are as a rule innervated 

 simultaneously, so that sensory impulses passing to the centres on 



