)U.(J.;:M\'i ^' I 



128 



THE PHYSIOLOGY OF NERVE 



effected by simply pinching the distal filaments of the nerve with forceps or by cut- 

 ting across them with the scissors. 



A very similar relationship exists in the electrical organ of Malapterurus. ^ In- 

 asmuch as its individual membranous plates are innervated by the branches of a 

 single motor nerve (Fig. 75), the mechanical stimulation of the terminals in a 

 single plate must invariably be followed by a discharge of the entire organ. Clearly 

 any impulse arising peripherally in one of these plates (D), can only be trans- 

 ferred to the adjoining plates (AB and C) at the next bifurcation, and hence, the im- 

 pulse must first asecnd along the normally efferent branch before it can spread in a 

 centrifugal direction to the other parts of the organ. This peripheral transfer of 

 impulses is made possible by the fact that the individual axis-cylinders of the motor 

 fibers divide when in close proximity to the end-organ and send their fibrillar com- 

 ponents in different directions into the tissue. 

 Consequently, it is not necessary that the reversed 

 impulse be transferred to a neighboring axis-cylin- 

 der, because it can reach its destination through 

 the fibrillae of the same axis-cylinder. It will be 

 seen, therefore, that conduction in both directions 

 is not contrary to the law of isolated conduction. 



Different investigators have also sought to 

 prove double conduction by the establishment of 

 a primary union between the central and distal 

 stumps of different sensory and motor nerves. 

 I I (I I Thus, it has been shown by Bidder (1865) that 



I I |\ j T a union between the distal end of the hypoglossal 



' (motor) and the central end of the lingual nerve 

 (sensory) eventually permits us to effect move- 

 ments of the tongue by stimulating the sensory 

 lingual nerve. In a similar way, Budgett and 

 Green^ have succeeded in cutting the left vagus 

 nerve between its ganglion and the cranium and 

 in uniting the peripheral stump of this nerve with 

 the peripheral end of the hypoglossal. Some 

 months later the muscles of the tongue could be 

 made to contract by stimulating the peripheral 

 end of the vagus. In this connection brief men- 

 tion should also be made of the well-known experi- 

 ment of Paul Bert 3 purposing the formation of a 

 primary union between the tip of the tail of a rat and the subcutaneous tissues 

 upon the dorsal aspect of its body. The process of healing having been fully com- 

 pleted, the tail was then cut off near its base. Inasmuch as the stimulation of 

 the former base of the tail still gave rise to sensations of pain, the conclusion 

 seemed justified that nerve- fibers conduct centripetally as well as centrifugally. 

 In all these experiments, however, it must be taken into account that the cutting 

 of nerves is followed by degeneration which in turn is succeeded by the formation 

 of new axis-cylinders. For this reason, it cannot be held that the inversion of a 

 part actually leads to an inversion of the nerve-fibers or to reversed conduction. 

 These experiments, therefore, cannot be said to be well adapted for proving 

 double conduction. 



Fig. 75. — Conduction in 

 Both Directions in the 

 Electric Organ of Malap- 

 terurus. 



N, motor nerve and its 

 branches, leading to plates A 

 B C and D; S, stimulation at 

 D produces discharges of entire 

 organ. 



The Speed of Conduction in Nerve. — Inasmuch as the passage of 

 the wave of excitation is not associated with visible changes, it was 

 thought at first that the rate of its progression, in analogy with that of 



1 Babuchin, Archiv fiir Anat. und Physiol., 1877, 262. 



2 Amer. Jour, of Physiol., iii, 1899, 115. 



3 Compt. rend., Ixxxiv, 1877, 173. 



