GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 139 



rent of equal strength is got if a new section be made by cutting off the tissue 

 injured by the first cut. In the case of the long-fibred muscles the death 

 process gradually progresses the length of the injured fibres, while in the case 

 of the heart-muscle, in which the cells are very short, the death processes are 

 limited to the injured cells, and on their death the current disappears ; when a 

 new cut is made other cells are injured and again a strong current is obtained. 



Dead tissue gives no current ; normal resting living tissue gives no current ; 

 dying tissue is electrically negative as compared with normal living tissue. 



Hering has carried Hermann's view that electrical change is the result of 

 chemical action still further. He considers that the condition of negativity is 

 an evidence of katabolic (breaking-down) chemical processes and that anabolic 

 (building-up) chemical processes are accompanied by a positive electrical change. 

 Like Du Bois-Reymond, he believes that the normal resting muscle may be 

 the seat of electro-motive forces which do not manifest themselves as long as 

 the different parts are in like condition. 



Current of Rest of a Nerve. Nerves like muscles show no electric currents 

 if normal and resting, but give a demarcation current if injured, the dying por- 

 tion being negative to normal parts, and the direction of the currents is the 

 same as in injured muscle. Gotch and Horsley 1 ascertained the electro-motive 

 force in the nerve of a cat to be 0.01 of a Daniell cell and of an ape only 0.005, 

 while in the spinal nerve-roots of the cat it was 0.025, and in the tracts of the 

 spinal cord of the cat 0.046 and of the ape 0.029. Larger currents are 

 obtained from non-medullated nerves, probably because a non-medullated 

 nerve contains a larger number of axis-cylinders than a medullated nerve of 

 the same size. The current of injury of a nerve lasts only a short time. The 

 death process which is the immediate result of the injury proceeds along the 

 nerve only a short distance, perhaps to the first node of Ranvier, and when it 

 has ceased to advance the current fails ; a new injury of the nerve causes 

 another demarcation current as strong as the first. 



Hering found that a nerve like a muscle could be excited by its own cur- 

 rent, provided the circuit between the longitudinal and fresh cross section of an 

 irritable nerve was rapidly closed. 



3. Currents of Action in Muscle. Just as the dying tissue of nerves is 

 electrically negative as compared with normal tissue, so active nerve- and 

 muscle-tissue is electrically negative as compared with resting tissue. 



Du Bois-Reymond discovered that if the normal longitudinal surface and 

 injured cut end of a muscle were connected with a galvanometer and the muscle 

 were tetanized, the magnet swung back in the opposite direction to the deflec- 

 tion which it had received from the current of rest. This backward swing of 

 the magnet was not due to a lessening of the current of rest, for if the effect 

 of the current of rest on the galvanometer were compensated for by a battery 

 current of equal strength and of opposite direction, so that the needle stood at 

 0, and the muscle were then tetanized, there was a deviation of the needle 

 in the opposite direction to that given it by the current of rest. Du Bois- 

 1 Philosophical Transactions, 1891, B., vol.182, pp. 267-526. 



