THE NERVOUS SYSTEM 



42 3 



Motor 



I Pressor 



Efferent 



I Secretory- 



Depressor 



Motor to skeletal muscle. 

 Vasomotor. 



Cardio-motor (not a true motor) . 

 Viscero-motor, and includes re- 

 spiratory (trachea and bronchi) 

 and coat of spleen. 

 Pilo-motor and unstriped muscle 



of skin generally. 

 1 Iris and ciliary muscle. 

 (" Salivary. 

 I Gastric. 

 I Sudorific. 



f Only known for heart, some 

 bloodvessels, some parts of 

 1 digestive canal, iris, and re- 



f Inhibito- 

 I motor 



tractor penis. 



Conduction in Nerves. — In considering the direction of the 

 impulses conveyed by nerves as a basis of classification, there 

 are two fundamental principles on which something more should 

 be said. It has been shown that the effect produced by a nerve 

 does not depend upon its structure, but upon the nature of its 

 termination in the tissue. Many years ago, before the truth of 

 this doctrine had been conclusively established, the writer had 

 endeavoured to cure a local paralysis by dividing the paralysed 

 nerve and suturing the peripheral end to the central end of a 

 sound motor nerve. He found that when two sound nerves were 

 so dealt with motor impulses from an entirely new source pro- 

 vided the tissue with motor function, and, moreover, furnished 

 it at the right moment — viz., at the moment the muscle was 

 required to contract, and not during the period when it should 

 relax. Subsequently Langley showed by a similar experiment 

 that the function of the chorda tympani and sympathetic on the 

 bloodvessels of the submaxillary gland could be reversed. If the 

 peripheral end of the sympathetic were united to the central end 

 of the chorda, the effect was constriction and not dilatation of 

 the vessels. Similarly, if the peripheral end of the chorda were 

 united to the central end of the sympathetic the vessels dilated 

 on stimulation of the sympathetic instead of contracting. The 

 essential structure was proved to be the nerve termination in the 

 tissue, and not the nerve which carried the impulse. 



It is on these lines that the writer has looked for the cure of 

 laryngeal paralysis in horses. But though he has succeeded, as 

 stated above, in getting a sound left recurrent sutured to a sound 

 spinal accessory to function properly, he has not succeeded in obtain- 

 ing these results with a paralysed left recurrent, not even when the 

 operation has been performed early, presumably before the end 

 plates had undergone complete degeneration. 



The other fundamental principle in nerve conduction relates 

 to the law that the living nerve only transmits impulses in one 



