PRESENT STATE OF ORGANIC ELECTRICITY. 337 



will be more or less directly centrifugal or centripetal as 

 long as the inducing current or power rotates the periphei-al 

 or the central dipolar molecule in each pair of double elec- 

 tromotor elements in the series, round an arc of from 90' to 

 180°. 



Tlic Electric Relations of Centrifitfjal ami Centripetal 

 Mrves are identical. — It would appear to be an important 

 residt of Du liois Reymond's electro-physiological researches 

 that motor and sensory nerves exhibit no difference in their 

 electrical relations. The electrotonic condition can be in- 

 duced in either direction. It may consequently be inferred 

 that a motor nerve is capable of conveying its mere influence 

 in either direction, but effectively only when it terminates in 

 a muscle. On the other hand, a sensory nerve is capable of 

 conveying its impression both ways, but with effect only 

 when it reaches a sentient centre. In so far as the investiga- 

 tion has been can-ied by employing electricity as the exciting 

 agent, Du Bois lieyiuond draws the following conclusion 

 from his experiments : " that in both kinds of nervous fibres 

 the innervation advances in both directions with equal 

 facility." * 



The Law of the Excitation of Nerves hy the Electrical Cur- 

 rent. — "When a uniform current is transmitted through the 

 nerve of the prepared Hmb of a frog, the leg contracts only at 

 the closing and opening of the circuit. In order to keep up 

 the contraction, or to produce a tetanic condition of the mus- 

 cles, the current must be variable or intermittent. The action 

 of a muscle is not, therefore, equivalent to the strength of the 

 the electric current which may be transmitted along its 

 nerve, but to the variations in it. The law is thus expressed 

 by Du Bois Bepnond : — " It is not the absolute value of the 

 density of the current in a motor nerve which corresj^nds to 

 the contraction of the muscle ; but the variation in this value 



• Unlersiu-Jiungen, vol. u. p. 590. 

 Z 



