1903.] Phenomena in Mammalian Non-medullated Nerve. 



177 



Median 



Fig. 8— Exp. 728, VIII. Anelectrotonic 

 and Katelectrotonic Currents, and Nega- 

 tive Variation on Mednllated Nerve. 



K=0 



Splenic. 



Fig. 9.— Exp. 729, A, VIII. The same 

 on Non-niedullated Nerve. An. and 

 kat. are too small to be legible, and 

 the negative variation only is seen. 



The voltage of the polarising current was § volt, the excitation 

 3000 units of the Berne coil, the distance between the centre of each 

 electrode and the next was 11 mm. 



In the medullated nerve the electrotonic currents exceeded the 

 negative variation ; in the non-medullated they were so small as to be 

 imperceptible on the photographic plate. In order to see whether 

 the electrotonic currents were completely absent, or merely very 

 small, further experiments were then made, using a higher voltage in 

 the polarising circuit. 



These measurements are uncertain, both from the difficulty of 

 measuring such very small currents, and from the fact that the cessation 

 of anelectrotonus and the commencement of katelectrotonus excite the 

 nerve, and the resulting negative variation in the latter case is added 

 to the katelectrotonic current, so that except in special cases (as in 

 Experiment 731) the readings of the latter are too high. It is also 

 not absolutely certain that current escape has not some share in the 

 result, though as all these effects are abolished by crushing the nerve, 

 and as the an- and katelectrotonic currents are not equal in magnitude, 

 and not exactly proportional to the polarising current, it is probable 

 that this error, if it exists, is a small one. 



Bearing these reservations in mind, certain conclusions may be 

 drawn from these experiments. The electrotonic currents in the 

 non-medullated nerves are evidently very small, about one -fortieth of 

 the same currents in medullated nerves. Further, while the an- and 

 katelectrotonic currents in the latter are nearly equal (0 ' 702 millivolt 



