INTESTINAL NERVE MECHANISM. 133 



centre, and thereby relaxation of the sphincter, while cold gives 

 rise to increased central action, causing contraction of the sphinc- 

 ter muscle (a point to be remembered when examining or oper- 

 ating within its grasp). Besides the voluntary variations which 

 we can bring about in the activity of this lumbar centre, many 

 other central influences, such as emotions, may operate upon it. 

 Thus terror inhibits the centre, and loosens the sphincter inde- 

 pendently of our will. 







