6i8 



bell's law and deductions thekefkom. 



may be divided without giving rise to complete anaesthesia in any part of the area of distribu- 

 tion of the sensory branches of the nerve, and even if there be partial or complete cutaneous 

 anaesthesia, it is much less in extent than corresponds to the anatomical area of distribution. 

 The anaesthetic area tends to become smaller in extent (Hoss). Thus, there is not complete 

 independence in the distribution of these nerves. These results are explained by the anas- 

 tomosis between branches of nerves, the exchange of fibres in the terminal networks, while some 

 sensory fibres enter the peripheral parts of a nerve and run centripetally, perhaps being distri- 

 buted to the skin and conferring recurrent sensibility on the peripheral part of the nerve.] 



Relative Position of Motor and Sensory Fibres. In embryos (rabbit) the motor fibres stain 

 more deeply with carmine than the sensory fibres, so that their position in the peripheral nerves 



of distribution may thereby be made out. In the 

 anterior branch of a spinal nerve, the sensory fibres 

 lie in the outer part of the branch, the motor in the 

 inner part ; while this relation is reversed in the 

 posterior root (L. Lowe). 



Deduction from Bell's Law. Careful ob- 

 servations of the effects of section of the roots 

 of the spinal nerves (Magendie, 1822), as well 

 as the discovery of the reflex relation of the 

 stimulation of the sensory roots to the ante- 

 rior, constituting reflex movements (Marshall 

 Hall, Johannes Muller, 1832), enable us to 

 deduce the following conclusions from Bell's 

 law : 1. At the moment of section of the 

 anterior root, there is a contraction in the 

 muscles supplied by this root. 2. There is at 

 the same time a sensation of pain due to the 

 " recurrent sensibility." 3. After the section, 

 the corresponding muscles are paralysed. 4. 

 Stimulation of the peripheral trunk of the 

 anterior root (immediately after the operation) 

 causes contraction of the muscles, and eventu- 

 ally pain, owing to the recurrent sensibility. 

 5. Stimulation of the central end is without 

 effect. 6. The sensibility of the paralysed 

 parts is retained completely. 7. At the mo- 

 ment of section of the posterior root, there 

 is severe pain. 8. At the same time move- 

 ments are discharged reflexly. 9. After the 

 section, all parts supplied by the divided roots 

 are devoid of sensibility. 10. Stimulation of 

 the peripheral trunk of the divided nerve is 

 without effect. 11. Stimulation of the central 

 end causes pain and rejiex movements. 12. 

 The central end ultimately degenerates. 13. 

 Movement is retained completely in the para- 

 lysed parts, e.g., in the extremities. 



The ultimate effect, known as Wallerian 



10 me 



Fig. 437. 

 Distribution of the cutaneous nerves of the 

 arm. A, Dorsal surface 1 sc, supra- 

 clavicular ; 2 ax, axillary ; 3 cps, supe- 

 rior posterior cutaneous ; 4 cmd, median 

 cutaneous ; 5 cpi, inferior posterior cu- 

 taneous ; 6 an, median cutaneous ; 7 

 cl, lateral cutaneous ; 8 u, ulnar ; 9 ra y 

 radial ; 10 me, median. B, volar sur- 

 face 1 



sc, supra-clavicular ; % ax 

 axillary; 3 cmd, internal cutaneous ; 4 , TTT^ ?T^F** 



cl, lateral cutaneous ; 5 cm, cutaneous degeneration, which follows section of the 

 medius ; 6 me, median ; 7 u, ulnar. nerve or its roots, is referred to in 325. 



Recently, Joseph has slightly modified the 

 statements of Waller on the degeneration in the posterior roots. According to him, 

 the spinal ganglion is the nutritive centre for by far the largest number of the fibres 

 of this root ; but individual fibres traverse the ganglion without forming connec- 

 tions with its cells, so that the nutritive or trophic centre for this small number of 

 nerve-fibres is in the spinal cord. 



