652 



PRINCIPLES OF GENERAL PHYSIOLOGY 



permeable to both ions of salts within the cell. It will be clear that the 

 demarcation current can only last as long as the contents of the injured 

 cell remain in place, and more or less identical in amount with what they 

 were normally. As soon as the electrolytes have been replaced by those of the 

 electrodes, owing to diffusion, the injured cells naturally become mere extensions 

 of the leading off electrodes, and, being in contact with the normal surface of 

 uninjured cells, the potential difference disappears. 



It is interesting to note that in tissues which contain as much as 99 per cent, of water, 

 such as those of the fresh water Medusa, investigated by Cremer (1906), an electrical change 

 in contraction can be detected. 



As an illustration of the phenomena in smooth muscle, we may take the 

 ureter, in which the electrical changes accompanying a wave of contraction 



FIG. 208. ELECTRO-CARDIOGRAM OF TORTOISE. Heart in^situ. Led 

 off from sinus and ventricle apex to capillary electrometer. 

 Movement of shadow upwards means negativity of sinus contact. 



A, Diphasic auricular response. 

 V, Diphasic ventricular response. 



Temperature, 12 C. 

 Time in jth sec. 



(Gotch, 1910, p. 237.) 



were recorded by Orbeli and Briicke (1910). Fig. 207 gives three of their 

 curves. In curve B one wave only is given, and is a copy of the actual 

 photograph as obtained. In curve A there are two waves, one of which 

 is marked for description. A movement downwards means that the electrode 

 under which the wave first passes becomes negative, and we notice that the 

 large wave Hj is in this direction, and that it is followed by another, H 2 , 

 in the opposite direction, as the wave of contraction leaves the first electrode 

 and arrives at the second. This corresponds exactly to what happens in nerve 

 and skeletal muscle. But what are the waves marked v and N ? It is suggested 

 by Orbeli and Briicke that they represent a wave of inhibition preceding the 

 contraction, as we have seen in the case of the intestine (page 367). It is clear 

 that, if the ureter were in a state of tonus or partial contraction, inhibition would 

 cause the first electrode to become less negative than the second, and appear 

 as a positive deflection. If, however, the deflection N is also due to progress 

 of the wave of inhibition . to the second electrode, as would appear from its 

 opposite direction, it must have travelled at a slower rate than the excitation 



