CHAPTER XYI. 



1. Various kinds of nerves ; 2, Absence of indicable differences 

 in the fibres ; 3. Characters of nerve-cells ; 4. Various kinds of 

 nerve-cells ; 5. Voluntary and automatic motion ; 6. Reflex 

 motion and co-relative sensation ; 7. Sensation and conscious- 

 ness ; 8. Retardation ; 9. Specific energies of nerve-cells ; 10. 

 Conclusion. 



1. At present we Lave paid attention only to such 

 nerve-cells as are in connection with muscles, and by 

 the activity of which the appropriate muscles are ren- 

 dered active. ^Ye have referred only incidentally to 

 other kinds of nerves. The difficulty due to the cir- 

 cumstance that a suitable reagent is necessary for the 

 study of such nerve-activity as does not express itself 

 in any visible change in the nerve, compelled us to con- 

 fine our studies in the first place to muscle-nerves or 

 motor nerves, in which the muscle itself acts as the 

 required reagent. We now have to discover how far 

 the experiences which we have gained of motor-nerves, 

 and the views which we have based on these experiences, 

 are applicable to other nerves. 



Besides the real motor nerves, we may distinguish 

 those which act on the smooth muscle-fibres of the 

 blood-vessels, through these effecting a decrease in the 

 diameter of the smaller vessels, and thus regulating the 

 circulation of the blood. These are called vaso-motor 

 nerves. They are, however, in no way different from 



