35 
wave of cciitraction suppressed in the region treated v. in 
KCl, but also the wave of excitation, inasmuch as no wave 
of contraction issues below the part affected — all parts of the 
intestine below that treated with KCl remain motionless, 
while those above that part are in vigorous peristalsis. This 
action of KCl in abolishing both contractility and excita- 
bility in the intestine of the fly is only an instance of its 
general effect upon contractile tissues, the cause of vvfiirh \\i\\ 
be discussed later. 
7. — On the Normal Presence of Anion-Proteid in 
Certain Tissues, and their Sensibility. 
A fact which it is important to realise is the normal 
presence of a certain amount of aniun-proteid in irritable 
tissues. It is easy to see that this is a priori probable, for, 
since the blood and lymph contain ions of both kinds, it is to 
be expected that some anions would be taken up and formed 
into anion-proteid. But confirmatory evidence is not far to 
seek : the cardiac inhibitory vagus fibres, when excited, pro- 
duce a positive variation of the muscle current ; this can only 
be due to anions released by the nervous impulse, and since 
"as regards their galvanic re-action to excitation they differ 
in no respect from other nerve fibres,"* these anions must be 
displaced from anion-proteid in the muscle itself, or in the 
nerve endings. The ''staircase" phenomenon, that is, the 
improvement of each of the first few contractions of a 
muscle by the one that precedes it, which is specially notice- 
able in the heart, and in the swimming bell of medusae,! is 
direct evidence of the fact that the wave of negativity is not 
propagated by mere diffusion ; for some chemical change evi- 
dently takes place wherever the wave passes, since the im- 
provement is not confined to the point stimulated, but occui^ 
at all points traversed by the wave of negativity. J I attri- 
bute the "staircase" to the presence of a small amount of un- 
stable anion-proteid, which tends to accumulate, and is mostly 
removed by the first few waves of negativity, the kations of 
which displace the anions. We should note that the ''stair- 
case" is not always comparable with the cumulative effect of 
sub-minimal stimuli on many tissues, so that they eventually 
become capable of causing discharge and evoking contraction. 
In this case, no doubt, the kations accumulate, being added 
* Bi^ederaiann : Elcctro-pliysiology, vol. ii., page 257. 
t Vide Romanes : Jellyfish, Starfish, and Sea-urchins, Int. 
sc, ser., page 56. 
T Romanes: Jellyfish, Starfish, and Sea-urchins. Int. 9C. 
ser., page 57. 
