v SPINAL COED AND NEEVES 293 



and motor nerves. Besides the motor nerves to skeletal muscles, 

 the motor nerves to plain muscle (intestine, excretory ducts, bronchi, 

 vessels), the secretory nerves, the inhibitory or dilatator nerves, 

 etc., must all be taken into consideration. All these nerves were 

 included in the common category of centrifugal or efferent nerves. 

 On the other hand, besides the nerves of general or specific sense, 

 the excitation of which produces conscious sensations, other nerves 

 that transmit impulses from the periphery to the centres, and do 

 not evoke any appreciable sensation, had to be recognised. Both 

 these groups of nerves were included in the general category of 

 centripetal or afferent nerves. The most general and compre- 

 hensive formula for the Bell-Magendie law must therefore run : 

 the ventral roots contain only centrifugal, the dorsal roots only 

 centripetal fibres. 



The first experiments of Bell, Magendie,and J. Miiller contain no 

 positive demonstration of this new and more comprehensive formula 

 of the law of the spinal roots. Yet (as already discussed in Vol. I. 

 Chap. X.) the results of experiments by Cl. Bernard, Schiff, 

 Pfliiger on vaso-constrictor nerves, of Dastre, Morat, Gaskell on 

 vaso-dilatators, of Luchsinger on the secretory sweat nerves, which 

 are all localised in the ventral roots, agree perfectly with it. 



Other investigations, however, showed that the Bell-Magendie 

 law in its wider formula is not universally valid, but admits of 

 certain exceptions. According to the work of Strieker and his 

 pupils, the vaso-dilatators to the posterior extremities are contained 

 in the 4th and 5th dorsal lumbar roots of the dog, and the corre- 

 sponding fibres for the anterior limbs run in the dorsal roots of 

 the brachial plexus. According to Steinach the motor fibres to 

 the oesophagus, stomach and intestine, including the rectum, are 

 contained in the dorsal roots of the 3rd- 6th spinal nerves in 

 the frog. This was disputed by Horton-Smith, who, however, 

 admitted that he had found motor fibres to the skeletal muscles in 

 the dorsal roots of the frog. These exceptions to the law agree 

 with the histological observations of Lenhossek and Eamon y Cajal, 

 who found that the dorsal roots contain centrifugal elements, i.e. 

 some cells of the ventral horn send out their axis-cylinders by the 

 dorsal roots. 



Magendie was the first to point out from certain of his experi- 

 ments that the dorsal roots sometimes contain motor fibres, and 

 the ventral roots sometimes contain sensory fibres. Owing to 

 these contradictory facts the value of the law of the functions of 

 the roots was disputed for some time ; but the difficulty dis- 

 appeared when Longet and then Bernard demonstrated that the 

 sensibility of the anterior roots was only an apparent exception to 

 the Bell-Magendie law. The sensory elements of the anterior 

 root really come from the dorsal root, and only pass through 

 the ventral to supply the sensory innervation of the meninges. 



