634 EVOLUTION OP HEAT, LIGHT, AND ELECTRICITY. 



the branch of the mesenteric vein proceeding from it, a decided deflection of 

 the needle was produced, indicating a positive condition of the blood; but that 

 no effect was produced when the second electrode was inserted into the artery 

 of the part instead of into its vein. These effects were found to cease after the 

 death of the animals ; and could not be attributed, therefore, to mere chemical 

 differences between the blood and the secreted product ; but must have arisen 

 from electric disturbance taking place in' the very act of secretion. 1 That the 

 process of Nutrition, as well as of Secretion, in parts which are undergoing 

 rapid molecular change, gives rise to electric disturbance, is proved by the ex- 

 periments of Matteucci and Du Bois-Reymond upon the relative electrical states 

 of different parts of muscles and nerves. If the two extremities of a muscle, 

 removed from the body of an animal very recently killed, be applied to the two 

 electrodes of a delicate galvanometer, there is usually some deflection of the 

 needle; this being greater in proportion to the difference in the arrangement of 

 the muscular and tendinous elements of the two extremities. Although the 

 direction of the current is constant for each muscle, yet there is no constant 

 relation between the direction of the currents and the position of the muscles in 

 the body; thus, in the gastrocnemius of the Frog's leg, the direction is from 

 the foot towards the body, whilst in the sartorius it is the reverse. Taking all 

 the muscles of a part together, however, there is usually such a want of balance 

 between the opposite currents, that a constant current is established in the 

 direction of the strongest and -most numerous of the separate muscular currents ; 

 this, in the Frog, passes uniformly from the hind-feet towards the head, and 

 was at one time supposed to be peculiar to that animal ; but a similar current 

 may almost always be detected in other animals. The muscular current grows 

 feebler and feebler, the longer the muscle has been removed from the body ; it 

 is affected by any agents which tend to lower its vitality, and becomes extinct 

 as soon as its contractility ceases. From the experiments of M. du Bois-Rey- 

 mond, to be presently described ( 670), it may be concluded that the current 

 in the arm of Man, when at rest, is from the shoulder towards the points of the 

 fingers. 



668. The conditions of the " muscular current" have been made the subject 

 of special investigation by M. du Bois-Reymond ; and the following is an out- 

 line of the results at which he has arrived, for whose due comprehension, how- 

 ever, it is requisite that the terms employed by him should be first defined. 

 The entire muscle being composed of a mass of fibres, having a generally parallel 

 direction, and attached at their extremities to tendinous structure, which has in 

 itself but little or no electro-motor power, but is a conductor of electricity, it 

 follows that the tendon or tendinous portion of a muscle represents a surface 

 formed by the bases of the muscular fibres considered as prisms, which may be 

 designated its natural transverse section. On the other hand, the fleshy surface 

 of the muscle, which is formed only by the sides of the fibres considered as 

 prisms, may be regarded as the natural longitudinal section of the muscle. 

 Again, if a muscle be divided in a direction more or less perpendicular to its 

 fibres, an artificial transverse section will be made ; whilst if the muscle be torn 

 lengthways in the direction of its fibres, an artificial longitudinal section will 

 be made ; and these artificial sections show the same electric conditions with 

 their corresponding natural sections. Now experiments repeated in a great 

 variety of modes demonstrate that every point in the natural or artificial longi- 

 tudinal section of a muscle is positive in relation to every part of its transverse 

 section, whether natural or artificial; the most powerful influence on the gal- 

 vanometer being produced, when a portion of the surface (or natural longitudinal 

 section) of a muscle is laid upon one of the electrodes, and a portion of the 



1 "Philosophical Transactions," 1848, p. 248. 



