38 



PHYSIOLOGY. 



Fig. 10. 



and the reverse obtains where death has occurred during full health. 

 As the rigor mortis comes on the contractility of the muscle departs. 

 Its cause is obscure, and may be complex, but its resemblance to the 

 contraction of fibrine after recent coagulation is strongly marked. 



The muscular fibres o^ organic life are very different, not only in 

 structure, but also in function, from those already described. They con- 

 sist of a series of tubes, which are not marked by transverse lines, and 

 in which the longitudinal striae are very faint. These tubes are 

 usually much flattened, and cannot be shown to contain distinct 

 fibrillge. They are generally smaller than those of 

 animal life, and sometimes present markings indica- 

 tive of a granular deposit. The nodosities upon their 

 surface are the nuclei of their original components. 

 (Fig. 10.) The peculiarity of these fibres is, that they 

 are very little subjected to nervous influence, and that 

 when stimulated to contraction by an irritant, they per- 

 form a series of vermicular movements gradually de- 

 creasing in intensity till perfect rest takes place. They 

 are found in the intestinal canal, ducts of glands, 

 middle coat of the arteries and bronchial tubes, &c. 



In every case muscular action must alternate with 

 intervals of rest. It is in these intervals that the re- 

 paration of the disintegrated tissue takes place, and 

 that the muscle recovers its contractility. 



The mechanical arrangement of the muscles upon the skeleton is 

 usually accompanied with a loss of power, but with a gain of velocity. 

 The locomotive framework may be regarded as a series of levers, of 

 which the fulcrum is generally a joint. In most cases the muscles 

 are attached near the fulcrum, as in the biceps. By this arrange- 

 ment a contraction of a single inch in the muscle, moves the hand 

 through the extent of a foot, but then the hand moves only with one 

 twelfth of the power exerted by the muscle. 



The nervous structure as it appears in the nervous trunks is an- 

 other example of the tubes with a secondary deposit. This is seen 

 in the white ov fibrous 7)iatter, wherever it occurs in the body, and 

 also in the fibres of the great sympathetic. In the ganglia we find 

 the other form of nervous substance, known by the name of the 

 gray or vesicular. Wherever these two kinds are united together, 

 they constitute a nervous centre. 



The ultimate nerve fibre — such as is seen in the spinal nerves — is 

 distinctly tubular. It consists of an external thin and delicate mem- 

 brane, which is nearly or quite homogeneous. It forms one complete 

 sheath, isolating the contained matter in its whole course from its 

 central to its peripheral extremity. This is called by Todd and Bow- 

 man the tubular tneruhrane. 



♦ 4. A muscular fibre of organic life with two of its nuclei (from the bladder). 5. The 

 same from the stomach. 



