46 
It has been shown that potassium salts produce a pro- 
longed contraction of the gastrocnemius muscle of a frog, 
while calcium salts and, to a lesser extent, sodium salts, 
antagonise this action of potassium salts. * We can easily see 
that this action of potassium salts is due to the faster diffusing 
kation augmenting the P.D. between the hyaloplasm and 
spongioplasm, and hence lowering the surface tension at the 
contact surface, and causing prolonged contraction, while the 
action of the Ca salts and Na salts is simply due to the fact 
that in them the anion usually moves faster than the kation. 
"The excitability of certain contractile substances (sper- 
matic filaments, ciliated cells) is considerably heightened by 
Na^CO^ in dilute solutions." " If the pelvic end of 
an uninjured curarised sartorius dips into a "5 — 1 per cent, 
solution of this salt, the excitability of the muscle to the 
closure of weak ascending currents is seen after a short time 
to be extraordinarily augmented, while the descending cur- 
rent still works quite normally, although break excitations 
are discharged with such low intensity of current and brief 
duration of closure as would not occur in normal muscle."! 
This improvement of contraction and excitability on treating 
with the Na^COg is, I believe, owing to its low positive 
stimulation efficiency slightly increasing the threshold num- 
ber, while the incoming kations enable a sufficient number to 
cause displacement to gather more quickly at any point. In 
my own experiments I have observed this improvement in the 
sartorious, in the semi-membranosus of the frog (fig. 7), and in 
the intestine of the fly. If a section of the fly's intestine be 
touched with decinormal Na.^COg, the peristaltic contrac- 
tions are much augmented at that part ; and, if the intestine 
be quiescent owing to long exposure to NaCl, peristaltic 
contractions will start at the point painted with Na^COg. 
The improvement, in both cases, quickly dies away, and the 
intestine becomes puckered at the part affected owing to 
increase of tone, this part now acting as if it had been 
painted with KCl. This is to be explained by the effect of 
the natrions being, at first, partly neutralised by the chlori- 
dions already present, and then as the natrions become pre- 
dominant the stimulation efficiency is too great, and the ion- 
proteids enter into persistent anabolism. 
* W. D. Zoethout: American Journal of Physiology, May, 
1902 : The Effects of Potassium aaid Calcium Ions on Striated 
Muscle. 
t Biodormanii : Klectro-physioLogy: Trans, by F. A. Welby, 
vol. i., page 221 
