CHAP. IL] THE CONTRACTILE TISSUES. Ill 



will be a current through the galvanometer from the former to 

 the latter; there will be a current of similar direction but of less 

 intensity when one electrode is at the circumference g of the trans- 

 verse section and the other at some point h nearer the centre of the 

 transverse section. In fact, the points which are relatively most 

 positive and most negative to each other are points on the equator 

 and the two centres of the transverse sections ; and the intensity of 

 the current between any two points will depend on the respective 

 distances of those points from the equator and from the centre of 

 the transverse section. 



Similar currents may be observed when the longitudinal surface 

 is not the natural but an artificial one; indeed they may be witnessed 

 in even a piece of muscle provided it be of cylindrical shape and 

 composed of parallel fibres. 



These ' muscle- currents ' are not mere transitory currents dis- 

 appearing as soon as the circuit is closed ; on the contrary they 

 last a very considerable time. They must therefore be maintained 

 by some changes going on in the muscle, by continued chemical 

 action in fact. They disappear as the irritability of the muscle 

 vanishes, and are connected with those nutritive, so-called vital 

 changes which maintain the irritability of the muscle. 



Muscle-currents such as have just been described, may, we re- 

 peat, be observed in any cylindrical muscle suitably prepared, and 

 similar currents, with variations which need not be discussed here, 

 may be seen in muscles of irregular shape with obliquely or other- 

 wise arranged fibres. And Du Bois-Reymond, to whom chiefly we 

 are indebted for our knowledge of these currents, has been led to 

 regard them as essential and important properties of living muscle. 

 He has moreover advanced the theory that muscle may be con- 

 sidered as composed of electro-motive particles or molecules, each 

 of which like the muscle at large has a positive equator and nega- 

 tive ends, the whole muscle being made up of these molecules in 

 somewhat the same way (to use an illustration which must not 

 however be strained or considered as an exact one) as a magnet 

 may be supposed to be made up of magnetic particles each with 

 its north and south pole. 



There are reasons however for thinking that these muscle- 

 currents have no such fundamental origin, that they are in fact of 

 surface and indeed of artificial origin. Without entering into the 

 controversy on this question, the following important facts may be 

 mentioned. 



1. When a muscle is examined while it still retains uninjured 

 its natural tendinous terminations, the currents are much weaker 

 than 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 



