292 PHYSIOLOGY CHAP. 



side, besides being insensitive, appeared to be completely paralysed; 

 but after a few minutes distinct movements were visible. In 

 other experiments Magendie cut the ventral roots on one side 

 and left the dorsal, when he noted that the corresponding limb, 

 while totally immobile and flaccid, preserved its sensibility intact. 

 He concluded that the posterior roots were more especially 

 connected with sensibility, the anterior roots more particularly 

 with movement. 



Magendie's experiments were the necessary complement to 

 those of Bell, who affirmed nothing as to the sensory properties 

 of either root. The merit of this discovery is undoubtedly shared 

 by both investigators. 



On repeating and varying his experiments, Magendie did not 

 always obtain such clear results as the above, and he published 

 his doubts with commendable scientific integrity. But they were 

 soon removed by the subsequent experiments of other workers on 

 animals more easily operated on than dogs. The most classical 

 demonstration of the Bell - Magendie law was given by Joh. 

 Miiller on the frog, in which it is possible to expose the entire 

 cord without serious functional depression. Mliller's frog, familiar 

 to every student of physiology, shows on one side complete 

 paralysis of movement with intact sensibility, on the opposite 

 side complete paralysis of sensibility with intact movements, 

 when all the ventral roots are cut on the one side, all the dorsal 

 on the other. 



The complete evidence for the Bell -Magendie law may be 

 summed up as follows : 



(&.) On exciting or dividing a ventral root, there is a 

 localised contraction in the muscle or muscles innervated by 

 that root. (&) The same effect is obtained on stimulating the 

 peripheral stump of the same ventral root by any stimulus, 

 (c) No effect, on the contrary, is obtained when the central stump 

 is stimulated, (d) Motor paralysis of the whole limb follows on 

 section of all the ventral roots that innervate its muscles. 

 (e) Signs of pain (cries, or more or less diffuse reflex movements) 

 are obtained on exciting or dividing any dorsal root. (/) The 

 same effect is produced by exciting the central stump of the same 

 divided root, (g) Excitation of the peripheral stump has no effect. 

 (Ji) After cutting all the dorsal roots that innervate a limb it is 

 found to be totally insensitive. 



The Bell- Magendie law holds for every class of vertebrate. It 

 was established for batracians by the experiments of Joh. Miiller, 

 Panizza, and Fodera ; for birds by those of Panizza, Moreau, and 

 Schiff ; for fishes by those of Wagner, Stannius, and Moreau. 



This original formula had to be revised as soon as it became 

 clear that the nerves of the sympathetic system, which serve the 

 viscerar organs, have as much a spinal origin as the somatic sensory 



