UNSTRIATED MUSCLE TISSUE. 473 



is brought about, which produces shortening of the fibres and the 

 same chemical changes as precede the coagulation. Before the 

 stage of coagulation appears, however, a chemical rearrangement 

 takes place, the result of which is the reconstruction of the un- 

 stable complex proteid. If nutriment be withheld, or if the stimu- 

 lation be too powerful, the recovery cannot take place, and we 

 find the muscle passing from a state of physiological contraction 

 to one of intense exhaustion, and then to coagulation and death. 





UNSTKIATED MUSCLE. 



So far reference has only been made to the skeletal muscles, 

 the fibres of which are marked by transverse striations, and whose 

 single contraction is extremely rapid and short. The contractile 

 tissues which carry on the movements in the various organs of the 

 body are not striated fibres, but, as has been already stated, con- 

 sist of elongated flattened cells with rod-shaped nuclei. They 

 occur generally in the form of sheets or layers forming coats for 

 the organs in which they lie. Their single contraction is slow 

 and prolonged, and commonly is transmitted from one muscle-cell 

 to another as a kind of sluggish wave. They are incapable of 

 passing into a tetanic state of contraction like striated muscles. 



The slowest contraction seems to be that of the little muscle- 

 cells in the walls of the bloodvessels. These remain in a state of 

 partial contraction, which undergoes a brief and partial rhythmi- 

 cal relaxation. The most forcible aggregate of unstriated muscle 

 elements is met with in the uterus. This organ, which has very 

 exceptional motor powers to perform, contracts in somewhat the 

 same way as the muscles of the bloodvessels, but more quickly 

 and with longer rhythmical intervals of partial relaxation. The 

 muscular wall of the intestine and the iris are among the most 

 rapidly contracting smooth muscles. 



The chemical properties of the smooth muscle are much the 

 same as those of striated skeletal muscles, and they pass into a 

 state of rigor, while dying, which seems to depend on the same 

 causes as the rigor mortis already described. 



40 





