GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 149 



difficult, therefore, to expose a muscle without injuring it ; but this can be done 

 in the case of the heart ventricle, and Engelmann showed that this gives no cur- 

 rent when at rest, although a current is found as soon as any part is hurt, the 

 part becoming immediately negative in relation to other uninjured parts. In 

 experiments on isolated, long, parallel-fibred muscles, the current which is 

 caused by the injury of one extremity is found to fade away only very gradu- 

 ally (it may last forty-eight hours or more), and this current can be strength- 

 ened but little by new injuries. In the case of the heart-muscle the current 

 caused by cutting off a piece of the ventricle soon disappears, but another cur- 

 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. 



HeringMias 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 injured muscle. The current of injury of a nerve lasts only a short 

 time. The death process which is the immediate result of the injury pro- 

 ceeds 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. 

 Gotch and Horsley 2 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 (X025, 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 olfactory nerve of the pike may give a current of 0.0215 to 0.0105 

 Daniell, while a piece of a frog's sciatic of equal diameter would give a cur- 

 rent of only 0.006 Daniell.' 



Hering found that an irritable nerve, like a muscle, could be excited by 



1 Hering: Lotos, 1888, Bd. ix.; translation in Brain, 1897. 

 » Philosophical Transactions, L891, B., vol. L82, pp. 267 526. 

 8 Knehne and Steincr : Heidelberger Untersuchungen, 1880, iii. S. 14U-169. 



