476 MANUAL OF PHYSIOLOGY. 



capable 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 blood vessels. 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 blood vessels, 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. 



