CHAP, ii.] THE CONTRACTILE TISSUES. 61 



when artificial transverse sections have been made; the natural 

 tendinous end is less negative than the cut surface. But the 

 tendinous end becomes at once negative when it is dipped in 

 water or acid, indeed when it is in any way injured. The less 

 roughly in fact a muscle is treated the less evident are the muscle- 

 currents, and it has been 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. 



2. Englemann has shewn that the surface of the uninjured in- 

 active 1 ventricle of the frog's heart is isoelectric, i. e. that 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 most 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. 



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 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 

 adduced in favour 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/ 



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 in a muscle whenever it 

 enters into a contraction. When currents of rest are observable in 

 a muscle these are found to undergo a diminution at the onset of a 



1 Th* necessity of its being inactive will be seen subsequently. 



