UNSTRIPED MUSCLE 



plasm, containing in its interior a rounded body, the 

 nucleus, specially distinguished by the affinity of parts of its 

 substance for colouring matters. To a body having this 

 essential structure, whatever its form, the name cell is 

 applied. 



Unstriped Muscle. — Examination of a teased preparation 

 of the muscular coat of the intestine, stomach, or urinary 

 bladder will show that it is com- 

 posed of delicate fibres (Fig. 31) 

 tapering at both ends, and with 

 a nucleus in the middle. These 

 are called smooth or unstriped 

 muscular fibres : they are ob- 

 viously cells which have under- 

 gone a great elongation in length. 



During the peristaltic move- 

 ments of the intestine (p. 75) each 

 fibre alternately contracts and 

 relaxes, becoming shorter and 

 thicker during the former pro- 

 cess, like the large muscles of 

 the body (p. 60). The move- 

 ments, in this case, however, are 

 not under the control of the will, 

 and unstriped muscular tissue is 

 therefore often spoken of as 

 involuntary muscle. 



Contractility of Protoplasm. 

 — We have now studied three 

 different kinds of movement in 



cells : — muscular movement in the unstriped muscle-fibres, 

 ciliary movement in the ciliated epithelial cells, and amceboid 

 movement in the colourless blood-corpuscles. Muscular 



Fir,. 31. — Unstriped muscular 

 fibres from the frog's intestine. 

 To the right are shown fibres from 

 the longitudinal and circular 

 layers (see Chap. VIII) cross- 

 ing one another ; to the left 

 isolated fibres. (After Howes.) 



