39 
for this ill the followinsf way: — The cause of the extra-polar 
wave of contraction is the accompanying ''wave of nega- 
tivity," which means that (in tlie first instance) when the 
wave of negativity approaches the kathode a number of kations 
are there set free. These kations will, however, be attract- 
ed by the katiiode, and, moreover, there will be very little 
undecomposed ion-proteid from which they can displace the 
ions : hence, the wave of negativity will be seriously hindered, 
and the proteid residues at the kathode will tend to retain 
some of the kations. At the anode, on the contrary, unde- 
composed kation-proteid is abundant, and the kations are not 
retarded by the action of the current itself, so that the wave 
of negativity passes this region without hindrance. 
We have seen that a certain amount of anion-proteid is 
present in muscle and nerve, consequently, on electrolysis 
taking place, anions are liberated at the anode : but, since 
kations are predominant, their number is not sufficient to 
cause displacement, and therefore a discharge ; while at the 
kathode the proteid residues cannot take up kations, for they 
are immediately dissociated ; but when the passage of the cur- 
rent ceases, the proteid residues at tne kathode immediatolv 
pick up kations; hence the concentration of free kations falls 
at this point, and kations diffuse in from other points, in- 
cluding the anode ; hence the mass influence of kations at the 
anode is diminished, the anions get the upper hand and create 
a discharge, which immediately, as we have seen, becomes a 
wave of negativity by displacement of kations. The concen- 
tration of kations at the physiological anode may, possibly, 
fall on break for other reasons ; thus some of the proteid resi- 
due at the kathode may, when the current is broken, take up 
the ions from the afljacent ion-proteicl : this may in turn re- 
coup itself from the next section, and so the area of diminish- 
ed kation concentration would travel to the anode. 
The question immediately arises : Have we any other evi- 
dence of the liberation of anions at the anode ? The answer 
is that we have ample m the phenomena of electrotonus. 
The effect of anions at the anode would be to lower 
erritabilifi/, because, in order to obtain a sufficient excess of 
kations over anions to create a discharge the influence of the 
free anions has to be neutralised; it will be to lower con- 
di/rflvity, because the anions will tend to prevent the incom- 
ing kations from displacing ions from the ion-proteid by 
lowering their mass influence : and it will be to cause "posi- 
tivity" in the region of the anode. These are the well-known 
phenomena of anelectrotonus."^ 
* T'7V7f Ootch : Sohlifer's Textbook of Physiolog:y. vol. ii., 
pages 494 and 502 : and BiedeiTnann : E!eotro-phvsiolos;v : Trans, 
by F. A AVelby, vol. ii., page 268. 
