MUSCULAR TISSUE. 



[CH. VI. 



the whole muscle is only the sum total of the contraction of all 

 the constituent sarcomeres. 



In an ordinary muscular fibre it is stated that when it con- 

 tracts, not only does it become thicker and shorter, but the light 

 stripes become dark and the dark stripes light. This again is 

 only an optical illusion, and is produced by the alterations in the 

 shape of the sarcostyles, affecting the 

 sarcoplasm that lies between them. 

 When the sarcous elements swell during 

 contraction, the sarcoplasm accumulates 



Fig. in. Termination of a 

 muscular fibre in a tendon- 

 bundle, m, sarcolemma ; s, 

 the same passing over the 

 end of bundle ; p, extremity 

 of muscular substance e, 

 retracted from the end of 

 sarcolemma tube ; t, ten- 

 don bundle fixed to sarco- 

 lemma. (Ranvier.) 



Fig. ii2. Three muscular fibres 

 running longitudinally, and 

 two bundles qf fibres in 

 transverse section, M, from 

 the tongue. The capillaries, 

 C, are injected, x 150. (Klein 

 and Noble Smith.) 



opposite the membranes of Krause, and 

 diminishes in amount opposite the sar- 

 cous elements ; the accumulation of sar- 

 coplasm in the previously light stripes 

 makes them appear darker by contrast 

 than the dark stripes proper. This 

 is very well shown in fig. no. There 

 is no true reversal of the stripings in the 

 sarcostyles themselves. 



That this is the case can be seen very well when a muscular fibre is examined 

 with polarised light. A polarising microscope contains a Nicol's prism 

 beneath the stage of the microscope which polarises the light passing through 

 the object placed on the stage. The eye-piece contains another Nicol's 

 prism, which detects this fact. If the two Nicols are parallel, the light 

 passing through the first passes also through the second ; but if the second 

 is at right angles to the first, the light cannot traverse it and the field 



