CHAP, ii.] THE CONTRACTILE TISSUES. 101 



muscle-currents ; and it is maintained that if adequate care be 

 taken to maintain a muscle in an absolutely natural condition, no 

 such currents as those we have been describing exist at all, that 

 natural living muscle is isoelectric, as it is called. 



2. The surface of the uninjured inactive ] ventricle of the frog's 

 heart, which is practically a mass of muscle, is isoelectric, no current 

 is obtained when the electrodes are placed on any two points of the 

 surface. If, however, any part of the surface be injured, or if the 

 ventricle be cut across so as to expose a cut surface, the injured spot 

 or the cut surface becomes at once powerfully negative towards 

 the uninjured surface, a strong current being developed which passes 

 through the galvanometer from the uninjured surface to the cut 

 surface or to the injured spot. The negativity thus developed in 

 a cut surface passes off in the course of some hours, but may be 

 restored by making a fresh cut and exposing a fresh surface. 



The temporary duration of the negativity after injury, and its 

 renewal upon fresh injury, in the case of the ventricle, in contrast 

 to the more permanent negativity of injured skeletal muscle, is 

 explained by the different structure of the two kinds of muscle. 

 The cardiac muscle, as we shall hereafter see, is composed of short 

 fibre-cells ; when a cut is made a c.ertain number of these fibre- 

 cells are injured, giving rise to negativity, but the injury done to 

 them stops with them, and is not propagated to the cells with 

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

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

 duces 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 untouched, uninjured muscles, that the 

 muscular substance is naturally, when living, isoelectric, but that 

 whenever a portion of the muscular substance 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 negative 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 



1 The necessity of its being inactive will be seen subsequently. 



