29 
It would thus appear that the structure of the sarcomere 
may be regarded as that represented in the diagram. If the 
walls of the sarcous element be elastic, it is obvious that the 
surface tension (T) of the fluid hyaloplasm would pull them 
in at all points along their surface of contact, while on dimi- 
nution of the surface tension the sarcous element would swell 
in order to increase tLe surface of contact, and, since nothing 
but hyaloplasm is available to fill up the space thus created, 
hyaloplasm will flow i7ito the sarcous element. If the surface 
tension is increased the operations would be reversed. 
I am aware that histologists are not unanimous in adopt- 
ing this theory of the structure of striated muscle, but it 
enables us to obtain a clear view of the influence of the sur- 
face tension of the hyaloplasm upon the contraction of 
muscle. 
5. — The Contraction of Striated Muscle. 
In order to explain the contraction of striated muscle we 
must assume that tliere is a contact difference of 'potential he- 
tween t/ie spongioplasm and hyaloplaf<m, due to the presence 
of kation-proteid i), the muscle. That kation-proteid is pre- 
sent in striated muscle is demonstrated by the second part of 
Hermann's law, namely, that muscle becomes negative when 
dying, that is, that within the muscle there is an E.M.F. 
tending to produce a current from the dying points to the 
other points in the muscle."^ If ''when dying" be taken to 
mean 'when injury of such a nature as to set up katabolism is 
applied" we may at once state that this is due to the libera- 
tion of kations by the decomposing ion-proteid. 
Similarly, muscle becomes "negative" when excited to 
activity, because the excitation sets up katabolism, and kations 
are set free. We shall go more fully into the influence of the 
electric current upon the kation-proteid in the sequel ; but, in 
passing, we may note Biedermann's statement that if the pas- 
sage of a weak "polarising" current through muscle be con- 
tinued, its excitability is first augmented and then dim- 
inished.! We can easily see that while the katabolic pro- 
cesses are being hurried up by the polarising current, any 
additional excitation will precipitate them the more easilv 
because the ion-proteid iS already partly decomposed, while, 
as the constant excitation and consequent katabolism continue 
the supply of kations becomes so diminished that it can no 
longer respond to the demands of additional excitation. That 
* For an explianation of this confusion in physiological ter- 
minology, vide WaUer: Human Physiology, 1896. page 388. 
+ Biedermann : Electro-physiology: Trans, by F, A. "Weiby. 
vol. i.. page 283. 
