THE MUSCULAR SYSTEM. 283 



when affected with cramps or spasms, becomes painful and very 

 sensitive to pressure. They are also endowed with an ex- 

 tremely delicate sense of feeling for their own state of con- 

 traction, so that they are capable of estimating very minute 

 variations in the force with which they act. The apparent 

 contradiction between these facts is easily accounted for, by 

 the consideration that the muscular nerves contain but very 

 few sensitive fibres, as is readily shown in the nerves of the 

 orbital muscles, &c. These fibres, to which probably belong 

 the few filaments above described, wdiich are distributed over 

 the whole muscle, though too scanty to render a muscle sen- 

 sible to local impressions, nevertheless suffice, when impli- 

 cated in the contraction of the entire muscular substance, to 

 convey to the sensorium the degree of pressure to which they 

 are subjected, and, when the organs are over-exerted, to induce 

 pain, in consequence of the frequently-repeated irritation which 

 they have undergone, or of the compression they endure from 

 the rigidity of the muscle. 



[The mechanical relations of the muscles have been excel- 

 lently treated of in the article by E. Weber (1. c), from which 

 the following conclusions may be drawn. The extent of the 

 shortening of the muscles amounts, in experiments upon 

 animals, on the average to fths, or in powerful muscles even to 

 |ths. The contractile force of a muscle does not depend, cceteris 

 paribus, upon its length, but solely on its transverse sectional 

 area ; that is to say, on that of all its primitive fasciculi, so 

 that a longer and a shorter muscle exert the same force, when 

 the sum of the transverse sections of all the fasciculi is the 

 same in both. According to the observations of Schwann and 

 Weber, the elasticity of the muscles diminishes at each con- 

 traction, and consequently the molecular motions, called into 

 play in them under the nervous influence, must be connected 

 with a change in their substance of an altogether peculiar 

 kind, which, however, can certainly only be regarded as a 

 secondary effect. The degree of contraction differs according 

 to the amount of antagonism with which it meets ; if the 

 latter be sufficiently powerful, no true movement of the limb 

 takes place, that is to say, the points of origin and insertion 

 of a flexor muscle (for instance) do not approximate; never- 



