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Life and Health 



77. Action of the Unstriated Muscles. The unstriated 

 muscles respond to irritation much less rapidly than do 

 the striated. The wave of contraction passes over them 

 more slowly and more irregularly, one part contracting 

 while another is relaxing. This may readily be seen in the 

 muscular action of the intestines, called vermicular motion, 

 or peristalsis. Irregular and excessive 

 contraction of the muscular walls of the 

 bowels produces the cramp-like pains of 

 colic. 



Experiment 18. To show the general appear- 

 ance of the muscles. Obtain the lower part of 

 a sheep's or calf's leg, with most of the lean 

 meat and the hoof left on. One or more of the 

 muscles, with their bundles of fibers, fascia, 

 and tendons, are readily made out with a little 

 careful dissection. 



The dissection should be made a few days 

 before it is wanted and the parts allowed to 

 harden somewhat in dilute alcohol. 



FIG. 31. A Spindle 

 Cell of Involuntary 

 Muscle. 

 (Highly magnified.) 



In the stomach the contraction of these 

 muscles produces the motion by which 

 the food is churned about ; in the arteries 

 and veins they regulate the size of the channels through 

 which the blood is driven along, and in the intestines they 

 supply the force by which the partly digested food is mainly 

 kept in motion. 



J 78. Muscular Contractility. The most characteristic 

 property of muscle in the living state is its contractility, 

 or the power of shortening when irritated by a stimulus, 

 its volume or bulk remaining the same. In brief, when a 

 muscular fiber contracts, it tends to bring its two ends 

 closer together. 



