APPARATUS OF MOTION IN GENEEAL. 121 



and these again of bundles of fibres more and more delicate, 

 until an elementary fibre, or what may be considered so, is 

 reached, and this can only be seen by means of the most 

 powerful microscope. It seems as if it were composed of a 

 series of discs. After death the muscular fibre is soft, and 

 easily torn ; during life it is firm and elastic. It is composed 

 essentially vt fibrin, to which is united albumen, osmazome, 

 and some salts. 



248. By means of certain stimulants, such as the will, 

 muscles contract ; that is, they swell, shorten themselves, and 

 become extremely hard ; the phenomena may readily be ob- 

 served by bending the fore-arm upon the arm. 



The mechanism by which this is effected has not yet been 

 discovered. One thing alone is certain, that the two extre- 

 mities of the fibre or muscle approach each other, and thus, 

 of necessity, act on whatever they may be attached to that is 

 moveable, displacing one or both, and of course the body 

 itself. Hence these organs have been called the active organs 

 of motion, in contradistinction to the bones, which are 

 passive. 



249. The muscles are attached to the bones by fibres of 

 great strength, insensible, and of a dead- white colour; they 

 are called tendinous or tendons ; when membraniform in their 

 arrangement they are called aponeuroses. 



250. Influence of the Nervous System on Muscular 

 Contraction. The muscles are the only parts of animals 

 which possess the faculty of contracting ; but this property is 

 displayed only through the influence of the nervous system. 



251. Influence of the Nerves. Each muscular fasci- 

 culus receives several nervous filaments. These proceed pa- 

 rallel with the fibres enclosed in a neurilemma; they also 

 pass transversely across the muscular fibres and form loops, 

 but how they terminate is not known. They seem to form a 

 continuous circle. 



By cutting the nerve across which supplies a muscle in a 

 living animal, the muscle becomes paralysed. By compressing 

 the brain of a living animal, all power of motion is lost. 



252. The nature of this influence of the nerves over the 

 muscles has been much investigated; and the inquiry led 

 Galvani and Volta to some brilliant discoveries. They proved 

 that electric currents, however produced, act on muscles in a 

 similar way to the will, producing contractions in them even 

 after death ; and so closely did the phenomena resemble each 



