45 
dipped into aii electrolyte with a positive 'stimulation ettici- 
eiicy" it would become negative at those points which are 
wetted, and we find this to be the case. If one end of a sar- 
torius that is free from current is briefly immersed in highly 
dilute solutions of K salts, that end becomes strongly "nega- 
tive" to the rest. This is simply neutralised by washing out 
with physiological NaCl solution. "^^ A glance at the table 
of stimulation efficiencies will show that all the salts of K 
used in physiology have positive "stimulation efficiencies.' 
The antagonistic action of NaCl is simply accounted for by 
the fact that it has a ntgafive "stimulation efficiency." That 
the action of NaCl in abolishing the "negativity" induced 
by K salts is really due to the fact of its anions diffusing 
faster than its kations is shown by the fact that Engelmann 
found that a solution of NaCl, if stronger than 6 per cent., 
produces a weak ■positivity" at points of a muscle immersed 
in it.f In face of the fact that nearly all potassium salts 
are highly positive stimuli — as shown by the table of stimula- 
tion efficiencies — it is difficult to deny that their highly 
poisonous effect, when applied to muscle, must be in some 
way connected with the high velocity of the K ion, and I 
think the explanation must be this : that when a muscle is 
dipped into too strong a solution of KCl, suppose, the kations 
diffuse so rapidly into the muscle-hyaloplasm and spongio- 
plasm that little or no contraction is evoked, for the muscle 
is now throughly permeated with potassium ions, and ion- 
proteicl cannot break down at any point without kations being 
immediately at hand to regenerate it. Even a strong cur- 
rent might not be able to liberate enough kations in any one 
section of the muscle to overcome the mass influence of those 
in the next ; in fact, potassium salts may be said to induce a 
state of "persistent anabolism" in the ion-proteid. Thus it 
would appear that the poisonous effect of potassium salts is 
primarily due to loss of conductivity in the muscle, owing to 
an excessive rise in the threshold number, and this view is 
fully borne out by my experiments on the intestine of the 
fly. If a section of the intestine is treated, in the manner 
described in Section 7, with decinormal KCl solution, a 
block is created at the points thus treated — no contraction 
can pass this area, and, moreover, the peristaltic contractions 
travelling down the intestine do not rea'}->pear heloio the 
affected area, hence the excessive rise of the threshold num- 
ber at the points treated with KCl renders propagation of 
the wave of excitation by displacement impossible. 
* Biedeniiann : Electro-physiology: Traais. by F. A. "Welby, 
vol. i.. page 354. 
t Ibid., vol, i., page 356. 
