THE PHENOMENA OF CONDUCTION IN NERVE 133 



to nerve tissue. Potassium salts depress. The same is true of mag- 

 nesium sulphate. Conduction may be temporarily blocked by means 

 of this salt and as effectively as by the application of ice or certain 

 narcotics. As a general anesthetic this salt is useless and dangerous.^ 



The most important agents influencing the activity of nerve- 

 tissue belong to the group of the anesthetics. Ether and chloroform 

 diminish the irritability and conductivity, the latter agent being a 

 more powerful depressant than the former. In these cases, the con- 

 ductivity usually persists for sometime after the excitability has been 

 thoroughly abolished. Alcohol diminishes the conductivity, but does 

 not materially affect the irritability. Carbon dioxid diminishes the 

 excitability and finally also the conductivity. Among the narcotics 

 opium, cocain, curarin and chloral hydrate act as depressants. The 

 conductivity of nerve may also be gradually destroyed by depriving it 

 of oxygen. This matter will be more fully discussed later on. Lastly, 

 the irritability and conductivity of nerve may also be varied by the 

 galvanic current. As this effect is of fundamental importance in 

 formulating ''Pfltiger's Law" and the ''Law of Unipolar Stimulation'* 

 of normal muscle and nerve, it will be more fully discussed later on. 



The Nature of Conduction. — In spite of the many views which have 

 been formulated in explanation of the cause of conduction by nerve, it 

 cannot be said at this time that the exact nature of this process has 

 been fully established. Thus, it has been suggested that a nerve- 

 fiber is a tube containing a liquid or luminiferous ether, which either 

 flows from place to place or oscillates back and forth. Others, 

 again, have compared the nerve-fiber to a metal wire and the wave 

 of excitation to a progressive charge of electricity. Still others have 

 stated that the excitation arises in consequence of an explosive chem- 

 ical change which then advances along the nerve-fiber. Without enter- 

 ing into a detailed discussion of these different views, it may be said 

 that they are based upon two fundamental conceptions, attaching to 

 conduction either a purely physical or a purely chemical nature. 



The adherents of the former theory claim that the wave of excitation 

 or nerve impulse is a physical force propagated along nerve-fibers 

 without the latter undergoing metabolic . changes. It has been sug- 

 gested, on the one hand, that it consists of a delicate quivering of the 

 molecular constituents of the nerve, and, on the other, that it is due to 

 a definite shear along the colloidal substance of the axis-cylinder. 

 An analogous process is the conduction of electricity along copper, 

 wires which necessitates no consumption of material. In accordance 

 with this theory, the nerve impulse consists solely of an electrical 

 wave which is known to pass along a nerve whenever it is activated. 



This entire process may be illustrated very convincingly with the help of the 

 so-called core-conductor, described by Hermann. ^ A thin platinum wire is 

 enclosed in a glass tube filled with a solution of zinc sulphate. In the several pairs 



^ Meltzer and Peck, Jour, of the Am. Med. Assoc, Ixvii, 1916, 1131. 



* Pfliiger's Archiv, v, 1872, 264; also see : Matteucci, Compt. rend., Ivi, 1863, 760. 



