780 



NERVE 



because the skin is bombarded by antidromic (p. 179) impulses dis- 

 charged from the inflamed ganglia. But an alternative hypothesis is 

 that a toxine spreads out along the nerves from the ganglia, just as 

 in traumatic tetanus the toxine is known to pass in the opposite direc- 

 tion along the nerves from the seat of injury to the central nervous 

 system. 



Classification of Nerves. Omitting the group of ' trophic ' nerves, 

 and the even more problematical ' thermogenic ' fibres (which some 

 have supposed to preside over the production of heat, and therefore 

 to assist in the regulation of the temperature of the body, but of 

 whose existence as distinct and specific nerve-fibres with no other 

 function there is not the slightest proof), peripheral nerves may be 

 classified as follows: 



Centripetal 



or afferent 



fibres. 



Smell. 

 Taste. 

 Hearing. 

 Sight. 



' Touch (light touch). 

 Pressure (perhaps in- 

 cluding the nerves of 

 muscular sense). 

 Warmth Cold. 

 Pain. 

 Calibre of small arteries 



(pressor, depressor). 

 Action of heart. 

 Respiratory movements. 

 Visceral movements. 

 Glandular secretion. 

 Ordinary skeletal 



muscles. 

 Skeletal muscles 

 Visceral 



/ Vaso -constrictor 

 I Cardio-augmentor. 

 Erector muscles of hairs (pilo-motor 

 fibres) . 

 ( Visceral muscles 



2. Inhibitory nerves for -j C Vaso-dilator. 



[Vascular ,, \ Cardio-inhibi- 



3. Secretory nerves { tory. 



* It is not known whether the afferent portion of a reflex arc is always com- 

 posed of fibres included in the first two categories, although undoubtedly in 

 some cases it is. 



I. Nerves of special sensation 



2. Nerves of general sensation - 



Possibly nerves other than 

 those included under i 

 and 2, concerned in 

 reflex changes in 



Centrifugal 



or efferent 



fibres. 



i. Motor nerves for 



Vascular 



PRACTICAL EXERCISES ON CHAPTERS XIII. AND XIV. 



i. Difference of Make and Break Shocks from an Induction Machine. 

 Connect a Daniell or other cell B (p. 697) with the two upper binding- 

 screws of the primary coil P, and interpose a spring key K in the circuit. 

 Connect a pair of electrodes with the binding-screws of the secondary 

 coil (Fig. 274). 



