THE PHENOMENA OF CONDUCTION IN NERVE 135 



mechanical energy, heat and electricity, but inasmuch as nerve serves 

 merely as an instrument of conduction, it cannot be expected to give 

 rise to considerable amounts of energy. It is a well-known fact that 

 there is no mechanical change in the active nerve and hence, the only 

 point for us to determine is whether it presents any indications of the 

 evolution of heat or electricity. So far it has not been possible to 

 demonstrate the occurrence of thermic changes with any degree of 

 certainty. Rolleston, 1 for example, employed a delicate bolometer in- 

 dicating differences in temperature of >ooo C., but no increase in 

 temperature could be detected. Negative results have also been ob- 

 tained by A. V. Hill 2 who made use of very sensitive thermoelectric 

 elements, indicating changes of a hundred millionth of a degree. 

 Cremer, 3 on the other hand, does not deny the possibility of thermo- 

 genesis, but states that the heat liberated by active nerve is less than 

 the Joule's heat of the stimulating current. Garten, 4 moreover, be- 



FIQ. 78. CURRENT OP INJURY IN NERVE. 



The cross-section of the nerve is galvanometrically negative to its longitudinal 

 surface. 



lieves it possible that the nerve possesses the power of quickly absorb- 

 ing the slight amount of heat developed in the course of its metabolism. 

 In the face of more recent observations, it can scarcely be denied that 

 nerve undergoes metabolic changes, and hence, in analogy with other 

 tissues, it may be inferred that nerve also liberates at least a slight 

 amount of heat. 



In contrast to these rather indefinite results, it has been fully 

 established that nerve liberates electrical energy. Thus, if the poles 

 of a galvanometer are connected with two separate regions of an un- 

 injured nerve, the needle remains perfectly stationary, proving thereby 

 that a normal nerve at rest is isoelectric or equipotential. But if 

 one of the non-polarizable electrodes is now adjusted to the cross- 

 section of this nerve, a deflection of the needle results at once (Fig. 78), 

 indicating thereby the existence of a demarcation current which we 

 call the current of injury, 5 While its strength equals only 0.02 volt 



1 Jour, of Physiol., xi, 1890, 208. 



2 Ibid., xliii, 1912, 433. 



3 Mtinchener med. Wochenschr., 1895. 



* Physiol. der markl. Nerven, Jena, 1903. 



6 Discovered by DuBois-Reymond in 1846 (Arch, fur Anat. u. Physiol., 

 1867, 417). 



