298 PHYSIOLOGY CHAP. 



innervation for a posterior limb, the movements of this limb, while 

 not abolished, will be altered in a characteristic manner. 



Panizza (1835), who first performed this experiment, noted 

 that the movements of the apaesthetic limb were uncertain and 

 showed the characteristics termed by us dysmetria, i.e. failure to 

 measure. In movements of flexion, for instance, the limb was 

 carried too far up and out. Stilling (1842) confirmed Panizza's 

 observations and ascribed to the dorsal roots the maintenance of 

 muscular tone by transmitting to the centres a knowledge of the 

 state and position of the muscles. Cl. Bernard (1858) pointed out 

 that the frog made little use of its leg muscles when the influence 

 of the sensory roots was cut out. A very accurate description of 

 the movements of the apaesthetic leg of the frog has recently been 

 given by the younger Hering. Among various phenomena he 

 noted the following as characteristic : when the animal jumps it 

 takes up its normal position first with the intact and then with 

 the apaesthetic limb, and in bringing the latter back to the 

 ordinary position raises it unduly (Hebphdnomen). When the 

 posterior roots are divided on both sides, the frog makes lower and 

 less extensive springs. 



The effects of dividing the dorsal roots in the dog were 

 exhaustively studied by Baldi (1885), who kept the animals alive 

 for a long time. On cutting the afferent roots of a hind-limb the 

 leg in which sensibility is paralysed is not used in walking during 

 the first days ; it seems incapable of supporting the weight of the 

 body, is kept semi-flexed at the thigh- and knee-joints, and is rarely 

 completely extended. Later the animal begins to use it in walking, 

 but in an abnormal manner ; it is lifted too high and thrown 

 either too far forward or too far back. After cutting the afferent 

 roots of the last three cervical nerves and the first thoracic on one 

 side, the animal limps, holding the insensitive leg up off the 

 ground. After a few days the leg may be used in walking, but 

 the foot gives way and the animal stumbles and falls. Sub- 

 sequently the gait improves, but then trophic disturbances of the 

 limb in which sensation is lost set in. Bilateral section of the 

 afferent roots of the lumbo-sacral plexus makes the animal 

 incapable of using the posterior half of its body, which is dragged 

 passively along by the anterior part as if paralysed. On lifting 

 the animal up, the hind-limbs perform alternate flexor and extensor 

 movements. Eventually the hind-limbs succeed in supporting the 

 weight of the trunk up to a certain point, but the knees often 

 knock together and give way. 



The effects of dividing the dorsal roots of the monkey, accord- 

 ing to Mott and Sherrington (1895), are even more striking. 

 When all the afferent roots of a limb are cut it is used neither in 

 walking nor climbing, and only comes into play with very energetic 

 movements of the corresponding normal limb. When the monkey 



