THEORIES OF DEMARCATION AND ACTION CURRENTS 801 



discharge (Reid and Macdonald), in the vagi accompanying the 

 movements of the lungs, in the oesophagus during swallowing, in 

 the cutaneous sensory nerves in response to the ' adequate ' stimulus 

 of pressure (Steinach), in the retina in response to the adequate 

 stimulus of light, in glands during secretion, in the central nervous 

 system during the passage of impulses along its conducting paths. 

 Some of these will be further considered a little later on. 



As to the interpretation of the facts we have been describing, 

 and which are summed up in the three propositions on p. 796, two 

 chief doctrines long divided the physiological world: (i) the theory of 

 du Bois-Reymond, the pioneer of electro-physiology, and (2) the theory 

 of Hermann. It was believed by du Bois-Reymond that the current 

 of rest seen in injured tissues is of deep physiological import, and that 

 the electrical difference which gives 

 rise to it is not developed by the 

 lesion as such, but only unmasked 

 when the electrical balance is upset 

 by injury. He looked upon the 

 muscle or nerve as built up of elec- 

 tromotive particles, with definite 

 positive and negative surfaces ar- 

 ranged in a regular manner in a sort 

 of ground-substance which is elec- 

 trically indifferent. The ' negative 

 variation' he supposed to depend on 

 an actual diminution of previously 

 existing electromotive forces; and 

 from this conception arose its his- 

 toric name. Hermann and his school 

 assumed that the uninjured muscle 

 or nerve is ' streamless,' not because 

 equal and opposite electromotive 

 forces exactly balance each other in 

 the substance of the tissue, but be- 

 cause electromotive forces are absent 

 until they are called into existence 

 (by chemical changes) at the boun- 

 dary, or plane of demarcation, be- 

 tween sound and injured tissue. For this reason du Bois-Reymond 's 

 current of rest is called in the terminology of Hermann the ' demarca- 

 tion ' current. 



The newer theories, such as Macdonald's, have sought to take account 

 of the recent developments of physical chemistry, and it is unquestion- 

 able that it is here the real explanation is to be found. There is little 

 doubt that the electrical phenomena of the tissues are connected with 

 the existence in them of membranes, envelopes, or sheaths, physiological 

 if not always anatomical, which are relatively impermeable to certain 

 ions. When such a sheath is injured, these ions, carrying with them 

 their electrical charges, may be supposed to migrate with abnormal 

 freedom through the injured part. A new distribution of electricity is 

 thus established in the tissue, and differences of potential depending 

 upon differences i n the concentration of the ions at different points are 

 set up. Bernstein and Tschermak, from an investigation of the thermo- 

 dynamic relations of bio-electrical currents, have come to the conclusion 

 that they are analogous to the currents produced by so-called concentra- 



Fig 292. Upper Curve, Record of the 

 Electrical Changes in the Vagus 

 Nerve (so-called ' Electrovagogram '), 

 taken with the String Galvanometer. 

 The small waves on it are synchronous 

 with the heart-beats, while the large 

 waves are synchronous with the respi- 

 ratory movements, the mechanical 

 record of which constitutes the 

 second curve (ascent, inspiratioi,). 

 The lowest curve is a mechanical 

 record of the pulse (Einthoven). 



