CHAP. IL] THE CONTRACTILE TISSUES. 109 



will be a current through the galvanometer from the former to the 

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

 sity when one electrode is at the circumference g of the transverse 

 section and the other at some point h nearer the centre of the trans- 

 verse 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 cur- 

 rent between any two points will depend on the respective distances 

 of those points from the equator and from the centre of the trans- 

 verse 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 repeat, 

 be observed in any cylindrical muscle suitably prepared, and similar 

 currents, with variations which need riot be discussed here, may be 

 seen in muscles of irregular shape with obliquely or otherwise ar- 

 ranged fibres. And du Bois-Reymond, to whom chiefly we are 

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

 gard 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 

 negative 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 muscle- 



