Physiology of the Muscles. 493 



tissue-;, whose movement is known to be caused by M like alteration of 

 Hie shape of their ultimate cells under stimulus. The fibres are not to 

 be supposed thrown into xigxag lines since fibres in this state, cannot be 

 supposed to exercise any force of traction. The very nature of the 

 strain would tend to straighten the elements if crooked. ( Neil & Smith's 

 Physiology. ) 



The blood vessels that supply the nourishment to the muscles, ramify 

 in the shape of delicate capillaries in the spaces between the fibres, but 

 do not themselves penetrate the sarcolemma, the nutrient matter being 

 absorbed by the cells through the membrane of the sarcolemma and 

 their cell walls, and the waste discharged by the converse process. The 

 motor nerves also penetrate the areolar tissue between the fibres, and 

 discharge their stimulus through that coat in a manner explained fur- 

 ther on. Once inside the sheath the stimulus is propagated along the 

 cells without again leaving the fibre, the sheath forming a sufficient in- 

 sulator. When a muscle fibre is stimulated at any point, it begins to 

 contract at that point, and a wave of contraction passes along the fibre 

 at the rate of from ten to thirteen feet per second. The pulsating vi- 

 brations which produce tetanus, do not have an} T effect if they exceed 

 about 800 to the second, as the ultra violet waves do not affect the eye. 



FIG. 232. a, Smooth-Muscle fibres. Mag- 

 nified 300 diameters. They are elongated, 

 spindle-shaped cells, having a nucleus near 

 the middle. 



Some are spirally twisted ( b ). 



In the smooth muscle, the fibres 

 consist of a series of tubes which 

 do not show any transverse marks 

 or striae. They cannot be subdi- 

 vided into fibrils. They are 

 smaller than the fibres of the vol- 

 untaiy muscles, and at intervals 

 along them there are nodules which 

 are the nuclei of the cells from 

 which they were originally derived. 

 Some have pointed ends, which 

 are sometimes twisted like a cork 

 screw ; and they have elongated 



FlQ 232 nuclei. They are destitute of the 



insulating sheath, or sarcolemma. They do not form separate masses 

 but occur scattered or arranged in more or less dense layers, or strata. 

 in almost all organs. These muscles are stimulated in their natural ac- 

 tion by the direct contact and . friction of substances, such as food ( in 

 the intestines ), blood ( in the arteries ), &c., and are but little under tSio 

 influence of the central nervous system. The peristaltic action . 



