574 



PROOFS OF DOUBLE CONDUCTION IN NERVES. 



where the nerve-fibre bifurcates in the muscle, and from thence centrifugally into 

 the other or non-stimulated apex, and causes it to contract. 



[The Gracilis of the frog is divided into a larger and smaller portion (L) by a 

 tendinous inscription (K) running across it (fig. 414). The nerve (N) enters at 

 the hilum in the larger portion, bifurcates, and gives a branch (k) to 

 the smaller portion and another to the larger portion of the muscle. 

 Let the muscle be cut as shown in fig. 414, avoiding injury to the 

 nerves, so that only the nerve-twig (k) connects the larger and smaller 

 portions of the muscle. If the tongue or tip of muscle (Z) with 

 its nerves be stimulated, contraction occurs both in L and M, which 

 is due to centripetal conduction in the motor nerve. The nerve-fibres 

 divide dichotomously above where the nerves are given off to the 

 portions L and M.] 



[If the inscription be left, and the lower tip of the muscle (which 



Fig. 414. is devoid of nerves) be stimulated, only the lower and not the upper 



Kiihne's Gracilis part twitches; but if a part of the muscle containing nerves common 



experiment. t0 both parts be stimulated, then both parts of the muscle contract. 



This also proves that pure muscular excitation does not travel backwards from the 



muscle to the nerves. How this comes about, we are entirely ignorant.] 



The following experiments used to be cited as proofs, but they do not stand the 

 test of criticism. 



4. Union of Motor and Sensory Nerves. If the hypoglossal and lingual nerves be divided in 

 a dog, and if the peripheral end of the hypoglossal be stitched, so as to unite with the central 



end of the liilgual (Bidder), then, 

 several months after the union and 

 restitution of the nerves, stimula- 

 tion of the central end of the 

 lingual causes contraction in the 

 corresponding half of the tongue. 

 Hence, it has been assumed that 

 the lingual, which is the sensory 

 nerve of the tongue, must conduct 

 the impulse in a peripheral direc- 

 tion to the end of the hypoglossal. 

 This experiment is not conclusive, 

 as the trunk of the lingual receives 

 high up the centrifugal fibres from 

 the seventh, viz., the chorda tym- 

 pani, which may unite with those 

 of the hypoglossal. Further, if the 

 chorda be divided and allowed to 

 degenerate before the above de- 

 scribed experiment is made, then 

 no contractions occur on stimu- 

 lating the lingual above the point 

 of union ( 349). 



5. Bert's Experiment. Paul 

 Bert removed the skin from the 

 tip of the tail of a rat, and stitched 

 it into the skin of the back of the 

 animal, where it united with the 

 tissues. After the first union had 

 Fig. 415. Fig. 416. Fig 417. taken place, the tail was then di- 



Double sponge rheophore. Disc rheophore. Metallic brush vid . ed at its base > so that the tail > 



as it were, grew out of the skin on 

 the back of the animal. On stimulating the tail, the animal exhibited signs of sensation. For 

 the explanation of this experiment, see 325. 



339. ELECTEO-THEEAPEUTICS REACTION OF DEGENERATION. Electricity is fre- 

 quently employed for therapeutical purposes, the rapidly interrupted current of the induction 

 machine, or Faradic current, being frequently used (especially since Duchenne, 1847), the 



