CHANGES IN A MUSCLE DURING CONTRACTION. 95 



with which they are in contact ; hence, upon their death, the negativity 

 and the current disappear. A fresh cut, involving new cells, produces 

 fresh negativity and a new current. In the long fibres of the skeletal 

 muscle, on the other hand, the effects of the injury are slowly propagated 

 along the fibre from the spot injured. 



Now, when a muscle is cut or injured, the substance of the fibres dies 

 at the cut or injured surface. And many physiologists, among whom the 

 most prominent is Hermann, have been led by the above and other facts 

 to the conclusion that muscle-currents do not exist naturally in un- 

 touched, uninjured muscles, that the muscular substance is naturally, 

 when living, isoelectric, but that whenever a portion of the muscular sub- 

 stance dies, it becomes, while dying, negative to the living substance, and 

 thus gives rise to currents. They explain the typical currents (as they 

 might be called) manifested by a muscle with a natural longitudinal surface 

 and artificial transverse sections, by the fact that the dying cut ends are neg- 

 ative relatively to the rest of the muscle. 



Du Bois-Reymond and those with him offer special explanations of 

 the above facts and of other objections which have been urged against 

 the theory of naturally existing electro-motive molecules. Into these we 

 cannot enter here. We must rest content with the statement that in 

 an ordinary muscle currents such as have been described may be witnessed, 

 but that strong arguments may be adduced in favor of the view that these 

 currents are not " natural " phenomena, but essentially of artificial origin. 

 It will, therefore, be best to speak of them as currents of rest. 



67. Current of action. Negative variation of the muscle-current. The 

 controversy whether the "currents of rest" observable in a muscle be of 

 natural origin or not, does not affect the truth or the importance of the fact 

 that an electrical change takes place and a current is developed in a muscle 

 whenever it enters into a contraction. When currents of rest are observ- 

 able in a muscle, these are found to undergo a diminution upon the occur- 

 rence of a contraction, and this diminution is spoken of as " the negative 

 variation " of the currents of rest. The negative variation may be seen 

 when a muscle is thrown into a single contraction, but is most readily 

 shown when the muscle is tetanized. Thus, if a pair of electrodes be 

 placed on a muscle, one at the equator and the other at or near the trans- 

 verse section, so that a considerable deflection of the galvanometer needle, 

 indicating a considerable current of rest, be gained, the needle of the gal- 

 vanometer will, when the muscle is tetanized by an interrupted current 

 sent through its nerve (at a point too far from the muscle to allow of 

 any escape of the current into the electrodes connected with the galvano- 

 meter), swing back toward zero ; it returns to its original deflection when 

 the tetanizing current is shut off. 



Not only may this negative variation be shown by the galvanometer, but 

 it, as well as the current of rest, may be used as a galvanic shock, and so 

 employed to stimulate a muscle, as in the experiment known as " the rheo- 

 scopic frog." For this purpose the muscles and nerves need to be very 

 irritable and in thoroughly good condition. Two muscle-nerve preparations, 

 A and B, having been made, and each placed on a glass plate for the sake 

 of insulation, the nerve of the one, B, is allowed to fall on the muscle of the 

 other, A, in such a way that one point of the nerve comes in contact with 

 the equator of the muscle, and another point with one end of the muscle or 

 with a point at some distance from the equator. At the moment the nerve 

 is let fall and contact made, a current viz., the "current of rest" of the 

 muscle A passes through the nerve ; this acts as a stimulus to the nerve, 

 and so causes a contraction in the muscle connected with the nerve. Thus, 



