THE PROPERTIES OF MUSCULAR TISSUE 101 



working in situ. In the former case there is no circulating blood 

 to carry the accumulating fatigue products away from the 

 muscle and so to delay the onset of fatigue. 



Physiology of Smooth Muscular Tissue. What has hitherto 

 been said applies especially to the skeletal muscles; but in the 

 main it is true of the unstriped muscles. These also are irritable 

 and contractile, but their changes of form are much slower than 

 those of the striated fibers. Upon stimulation, a longer period 

 elapses before the contraction commences and when, finally, this 

 takes place it is comparatively very slow, gradually attaining a 

 maximum and gradually passing away. 



Unstriped muscular tissue has a remarkable power of remain- 

 ing in the contracted state for long periods: the muscular coats 

 of many small arteries, for example, are rarely relaxed; some- 

 times they may be more contracted, sometimes less, but in health 

 seldom if ever completely relaxed. 



There are in the body a number of sphincters, circular bands 

 of smooth muscle which guard the openings of various organs 

 such as the stomach, large intestine, and bladder. These are 

 strongly contracted the greater part of the time, relaxation being 

 for them only an occasional occurrence. They maintain their 

 condition of strong contraction without fatigue and apparently 

 without much expenditure of energy, offering in this regard a 

 sharp contrast to skeletal muscle. 



