ELECTRICAL RELATIONS OF MUSCLE. 



813 



Mansvelt, however, deduces as the principal result of his experiments, 

 that living muscle is, at least within certain limits, extended in proportion 

 to the increase of the weights, each fibre elongating about 1 per cent, of its 

 length for each 65th of a grain weight appended to it. According to 

 Wundt, the weight which is required to extend a fresh muscle of 1 square 

 millimetre (Jjth of an inch) sectional area, twice its length, is 2 oz. The 

 muscles are constantly in a state of slight tension, as is shown by the separa- 

 tion of their extremities when cut ; but it would obviously have seriously 

 interfered with their action had a high degree of elasticity been conferred 

 upon them, since antagonistic muscles would have had this, in addition to 

 all other resistances, to overcome, before movement could be effected. 

 Weber has shown that the extensibility of muscles increases during con- 

 traction. He applied a weight of 115 grains to an elongated muscle. On 

 the addition of another weight of 15J grains, the amount of extension which 

 took place was about y^ of its length ; but on repeating the same experi- 

 ment with a contracted muscle, the extension was as much as ^ of its 

 length, showing that the extensibility was greater in the latter case than in 

 the former. The exhaustion of a muscle greatly increases its extensibility 

 up to a certain point, after which it again diminishes. Thus, when a por- 

 tion of muscle was weighted with 115 grains, its greatest extension occurred 

 when it had been made to contract 43 times; when weighted with 193 grains, 

 after 23 contractions; and lastly, when weighted with 424 grains, at the 8th 

 contraction. It was even found that, by appropriate weighting, a muscle 

 on being stimulated to contract might actually become longer instead of 

 shorter. 



664. Electrical Relations of Muscle. As we have already seen in the 

 Nerves ( 472), so in the Muscles it is easy to furnish evidence of electrical 

 disturbance. The conditions of the "Muscular current" have been made 

 the subject of special investigation by M. Du Bois-Reymond ; and the follow- 

 ing is an outline of the results at which he has arrived, for the due compre- 

 hension of which, however, 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 extremi- 

 ties 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 ten- 

 dinous 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 



