GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM. 193 



of its nutrition on a nerve-cell since, if divided in its course, 

 the part separated from the cell rapidly degenerates. It 

 might also be urged that secretory nerves are trophic nerves 

 in the true sense of the word, since when excited they 

 cause the secretory cells to live in a special way, and produce 

 substances which when unacted upon by their nerves they 

 do not form. But if we call secretory nerves trophic we 

 must include also under that name all other efferent nerves; 

 the nutritive processes going on in a muscular fibre when at 

 work are different from those in the same fibre when at rest, 

 and the same is true of all other cells the activity of which is 

 governed by nerve-fibres. 5. Peripherally -act ing inhibitory 

 nerves, such as those which slow or stop the beat of the heart. 



Intercentral Nerve-Fibres. These, which do not convey 

 impulses between peripheral parts and nerve-centres, but 

 connect one centre with another, form a final group in addi- 

 tion to efferent and afferent nerve-fibres. Many of them 

 connect the sporadic and sympathetic ganglia with one an- 

 other and with the cerebro-spinal centre, while others place 

 different parts of this latter in direct communication; as for 

 instance different parts of the spinal cord, the brain and the 

 spinal cord, and the two halves of the brain. The paths taken 

 by some of these commissural fibres will be stated in connec- 

 tion with the physiology of the brain and spinal cord. 



General Table. We may physiologically classify nerve- 

 fibres as in the following tabular form, which is founded upon 

 the facts above stated. 



Nerve-fibres. 



Peripheral. 



f Suasory. 



Afferent. 



Efferent. 



Excito-motor, 

 Inhibitory. 



[ Motor. 

 | Vaso-motor. 

 \ Secretory. 

 I Trophic. 

 Inhibitory. 



Intercentral. 



Inhibitory. 



The Electrical Phenomena of Nerves. Under certain 

 conditions electrical currents can be led off from living nerve- 



