NERVE. 



By FRANCIS GOTCH. 



CONTEXTS: FUNDAMENTAL CHARACTERISTICS OF NERVE PHENOMENA.- General 

 Review of Nerve Functions, p. 451 Phenomena of the Excitatory State, p. 453 

 Metabolism during Activity, p. 453 Conductivity of Nerve, p. 455 Trans- 

 mission in both Directions, p. 456 THE EXCITATION OF NERVE. Modes of 

 Stimulation, p. 459 Induced Currents, p. 459 Undulatory Currents, p. 461 

 Condenser Discharges, p. 461 Galvanic Currents, p. 462 Unipolar Excitation, 

 p. 463 Chemical Excitation, p. 464 Mechanical Excitation, p. 467 Condi- 

 tions determining the Efficiency of Stimuli, p. 468 Law of Excitation, p. 469 

 Influence of Direction of Electrical Currents, p. 472 Nerve Indefatigability, 

 p. 473 Limits of Excitation by Repeated Stimuli, p. 474 THE CIRCUM- 

 STANCES AFFECTING NERVE EXCITABILITY AND CONDUCTIVITY. Maintenance of 

 Circulation, p. 477 Maintenance of Continuity with Nerve-Cells, p. 478 

 Comparison of Different Nerves and Different Parts of same Nerve, p. 480 

 Alterations of Temperature, p. 484 Chemical Reagents, p. 487 Anaesthetics, 

 p. 491 Polarisation Changes, p. 493 POLAR EXCITATION OF NERVE BY ELEC- 

 TRICAL CURRENTS. Pfliiger's Law of Contraction, p. 503 Influence of Duration, 

 etc., p. 505 Causation of Polar Excitation, p. 507 Closing and Opening 

 Tetanus, p. 510 Polar Excitation in Crayfish Nerves, p. 512 In Man, p. 515 

 In Peripheral Sense Organs, p. 516 ELECTROMOTIVE CHANGES IN UNEXCITED 

 NERVE. The Nerve Current, p. 518 Its Production, p. 519 Influence of 

 Various Conditions on its Amount, p. 520 ELECTRO-MOTIVE CHANGES IN 

 EXCITED NERVE. The Negative Variation, p. 524 Its Discontinuous Char- 

 acter, p. 527 Electrical Response to One Stimulus, p. 529 Influence of 

 Various Conditions, p. 533 After-Effects, p. 537 ELECTROMOTIVE CHANGES 

 ASSOCIATED WITH PASSAGE OF CURRENTS. External and Internal Polarisation, 

 p. 540 Electrotonus, p. 546 Influence of Physiological Changes upon Electro- 

 tonus, p. 550 Excitatory After-Effects, p. 556 Polarisation and Excitation, 

 p. 557. 



THE FUNDAMENTAL CHARACTERISTICS OF NERVE PHENOMENA. 



General review of nerve functions. The physiological phenomena 

 exhibited by nerve may be considered under three different aspects, 

 indicated by the terms " excitability," " conductivity," and the " state of 

 excitation." 



Excitability is pre-eminently the attribute of nervous tissue ; hence 

 the phenomena of nerve comprised under this expression represent more 

 definitely than those of other excitable structures the conditions which 

 determine its possession, and the circumstances which modify its mani- 

 festation. A tissue is said to be excitable if it responds by the develop- 

 ment of specific changes to the local action of external change in its 

 immediate environment. The altered condition thus produced is termed 

 " the excitatory state," whilst the external agent which has evoked this 

 is termed the " stimulus " or " exciting cause." 



