60 MUSCLE CURRENTS. [BOOK i. 



If they are quite equidistant, as for instance when one is placed on 

 one cut end x, and the other on the other cut end y, there will be 

 no current at all. 



If one electrode be placed at the circumference of the transverse 

 section and the other at the centre of the transverse section, there 

 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 transverse 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 repeat, 

 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 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 largely into the 

 controversy on this question, the following important facts may be 

 mentioned. 



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

 its natural tendinous terminations, the currents are much less than 



