51 
In general, inhibition must be due to an income 
of anions large enough to neutralise the kations present, 
but not strong enough to cause a discharge in addi- 
tion. If inhibition in the heart were due to the refractory 
period after a subminimal discharge of kations it could not 
last 252 seconds after stimulation of the vagus, as it may do.* 
We should expect the anions to cause a relaxation, and this 
takes place, t We should expect excitation of the inhibitory 
nerve, if it sets free anions in the muscle, to cause 'positi- 
vity" at the points affected, and this is the case.| All doubt 
as to the action of the inhibitory fibres of the vagus being 
comparable to the effect of free anions at the parts affected — 
that is, to anelectrotonus — is removed by the fact that "a 
crystal of salt applied to the sinus will produce Lhe same 
electrical variation as stimulation of the vagus nerve/"' § since 
in NaCl the stimulation efficiency is negative. In some 
animals the contractions of the ventricle are not diminished 
by vagus stimulation, hence there must be few or no anions 
at the vagus nerve-enaings in the ventricles of these animals, 
and a most remarkable confirmation of my theory as to the 
nature of the 'staircase"!! and of inhibition is that ''another 
somewhat unexpected coincidence is brought out by the com- 
parison of ventricular muscle, whose contractions are 
diminished by vagus stimulation and ventricular 
muscle, whose contractions are not so diminished, 
namely, that the staircase phenomenon obtains 
only in the former case, and not in the latter." U The efiPect of 
the anions liberated by the inhibitory nerve in the heart will 
be to depress the 7'ate of the contractions, because a greater 
number of kations will have to gather at each point to over- 
come the mass influence of the anions. To depress the con- 
ductivity owing to the state of anelectrotonus induced, and 
to diminish the force of contractions owing to the diminished 
tonicity : all these are known effects of stimulation of the 
inhibitory nerve. *"'*■ The auriculo-ventricular ring always 
specially tends to block contractions — we may assume that 
* Gaskell : Schafer's Textbook of Physiology, vol. ii., page 
207. 
t Ihid., page 210. 
t Biedennann : Electro-physiology, vol. ii.,, page 257. 
§ Gaskell : Schafer's Textbook of Physiology, vol. ii., page 
223 
II Tide section 7, this paper. 
IT Gaskell : Schafer's Textbook of Physiology, vol. ii., page 
214. 
** Ibid., vol. ii., page 209. 
