52 
this is due to an abundance of anions in this part — hence if 
we cut off the supply of kations, by ligaturing the coronary 
arteries, a block takes place,* because the anions have now- 
got the upper hand. 
The augment or nerves increase the rate of rhythm, be- 
cause kations are more abundant, and therefore at the initial 
jDoints of contraction they more quickly reach the threshold 
number. The force of contractions increases because of in- 
creased tonicity. Conductivity increases because the inhibi- 
tory action of the anion-proteid normally present is overcome 
by the free kations : that is, presuming that the augmentor 
nerves end in spots where anion-proteid is scarce, and that 
the impulse therefore sets free kations : and all these are 
known effects of stimulating the augmentor nerve fibres, t 
The alteration in tone and the negative variation produced 
by stimulating the augmentor fibres is slight. X This is to be 
expected, otherwise a discharge would be initiated at the 
nerve endings, and the refractory period would diminish con- 
ductivity. The discharge by the augmentor fibres must be 
less than the threshold number. 
The after-effect of inhibitory nerves in improving con- 
ductivity § is probably due to increased instability of the ion- 
proteid, the after-effect of the augmentors to the reverse. 
The facts we have considered throw light on the whole 
action of antagonistic nerves in the many cases where there is 
a double nerve supply. 
14. — Rhythmicity in Nerves. 
One of the best examples of rhythmicity in nerves is that 
of Ritters opening tetanus. '"An indirectly excited muscle 
may, after prolonged closure of a powerful battery current, 
fall, on breaking the circuit, into a state of persistent tetanic 
excitation." || It specially occurs in "cooled frogs," when, as 
we saw in section 7, the threshold number is great, and the 
nervous impulse which gives rise to tlie tetanus is rhythmic.H 
There can be little doubt that this is a rhythmic discharge 
due to a collection of anions at the anode, just as a rhythmic 
* Gaskell : Schafer's Textbook of Physiology, vol. ii., page 
193. 
t Ihid., vol. ii., page 216. 
I Ihid., vol. ii., page 218. 
§ Ihid., vol. ii., page 220. 
II Biedennann : Electro-physiology: Trans, by F. A. Wei by, 
yol. ii., page 117. 
II Ih'id., vol. ii., page 119. 
