x ELECTROMOTIVE ACTION IN NERVE 229 



ill the spinal cord to 0'046 Dan., and 0'029 Dan. in monkey. 

 Comparison of the spinal cord of young full-grown animals with 

 the large nerve of adults proves that this is not due solely to the 

 greater sectional area. 



In all experiments upon the so-called current of rest in the 

 nerve (Hermann's " demarcation current "), it is essential that the 

 lead-off from the cross-section should be as clean as possible. It is, 

 of course, more difficult to lead off from the transverse section of 

 finer nerves than from coarse trunks. Hence it becomes advisable 

 to destroy a certain tract near the transverse section, and to 

 lead off from the dead end. Under conditions in which the 

 demarcation current of the frog's sciatic yields at most a galvano- 

 meter deflection of about 70 degrees, Biedermaun obtained 

 deflections of 60-200 degrees from the two juxtaposed nerves 

 of mollusca, the diameter being still considerably below that of 

 a single frog's nerve. In non-medullated nerve also there is 

 a zone of rapidly diminishing negativity near the demarcation 

 surface, which again produces " weak longitudinal currents " 

 (Biedermann. supra, also Kuhne and Steiner). 



The reaction of nerves that are different in function is very 

 striking on leading off from two cross-sections, when the current 

 should be zero, if the negativity on both sides were equal. This 

 is not, however, the case (du Bois-Eeymond, 6) : a difference of 

 potential occurs not merely in the frog's sciatic, but also in the 

 nerves of warm-blooded animals (Fredericq, 1, p. 68, note). 



Mendelssohn (6) subsequently found regular and apparently 

 constant differences of negativity between any two cross-sections 

 in pure centripetal or centrifugal nerves. Du Bois-Eeymond 

 had already in electrical nerves shown greater negativity of the 

 peripheral cross-section as compared with the " equator," so that 

 the current from section to section, the so-called " axial current," 

 is always in an ascending direction. The same is true, according 

 to Mendelssohn, of the (purely centrifugal) muscular branches of 

 the rabbit's sciatic ; while in the posterior roots of frog and rabbit, 

 as also in the optic and olfactory nerves of the fish, the axial 

 current is descending. In the mixed trunk of the sciatic, again, 

 the direction is alternating. If any law could be formulated 

 from these observations, it would be that the axial nerve current 

 is opposed in direction to the physiological action of the nerve 

 fibres. These observations may conceivably be brought into line 



