37 
ed by lowering the temperature.^ This means that /i is 
raised, therefore the excitability to short-duration stimuli is 
lowered, t Since conduction is much slower in smooth than in 
striated muscle, /i must be greater in the former, and the 
minimal duration of excitation, in order to cause contraction, 
is therefore greater in smooth than in striated muscle. And, 
indeed, Biedermann states generally that the excitation of 
more sluggish excitable tissues depends on the duration of the 
stimulus.. I The conductivity of muscle is lowered by lower- 
ing the temperature, but the height of the contractions is 
augmented :>< this is because of the greater value of fi caus- 
ing a greater P.D. on excitation. Since the rate of propa- 
gation in the heart is less than in striated skeletal muscle (1"5 
metres per sec, as against 3 metres per sec.)|| (i is pro- 
bably greater in heart muscle than in ordinary striated 
muscle. 
8. — Polar Excitation in Muscle and Nerve and 
Electrotanus. 
One of the most striking facts in the electrical stimula- 
tion of muscle is that the make contraction starts at the 
kathode, and the break contraction at the anode. From my 
theory, however, it seems to obtain a sufficiently simple ex- 
planation. On the passage of the electric current the ion- 
proteid undergoes decomposition, and, in accordance with 
the laws of electrolysis, kations collect at the kathode. As 
soon, however, as the kations at the kathode reach the 
''threshold number" they displace the kations from the adja- 
cent section of ion-proteid material ; these, in turn, displace 
the kations from the next section, and so the wave of nega- 
tivity is propagated through the tissue. This view of the 
nature of the ''wave of negativity" obtains further support 
from the fact that "the responsitivity of the kathodic points 
of fibres in a muscle traversed by a current increases, up to 
a certain limit, with the intensity of the polarising current. 
This limit, however, is very low . . . beyond this limit 
excitability diminishes, as has been shown, in proportion 
with the strength of the polarising current." ^ Suppose a 
* Gotch: Schafer's Textbook of Physiology, vol. ii., padres 
486 and 534. 
t Ihid., vol. ii., page 485. 
+ Biedennann : P]lectro-physiolo2;y, vol. ii., page 106 
§ Ihid., vol. i., page 98. 
II Burdon Sandensoiii : Schafer's Textbook of Phy.^ioiog^, 
Tol. ii., pages 383 and 443. 
•Biedermann: Electro-physiology: Titins. by F. A. Welby, 
vol. i., page 285. 
