THE NERVE-NET 129 



tractions. In fact, Mall (1896 a) has shown that a piece 

 of small intestine may be removed from the body, kept on 

 ice twenty-four hours, and on being perfused in a warm 

 bath, will contract rhythmically, an observation coirimned 

 in its essentials by Cannon and Burket (1913). The small 

 intestine must, therefore, be admitted to exhibit a high 

 degree of autonomy. Magnus (1904) has attempted to ob- 

 tain evidence as to the location of the layer or layers con- 

 cerned with this autonomy. If a piece of intestinal wall 

 is split so as to remove the mucosa and submucosa with 

 the submucous plexus, the remaining portion will exhibit 

 all the reactions that the section, of the intestine before 

 the removal showed. Hence it is believed that the sub- 

 mucous plexus is not necessary for the essential move- 

 ments of the intestines. If, now, the remaining portion is 

 separated into two sheets, one including the circular 

 muscles and the other the myenteric plexus and the longi- 

 tudinal muscles, that containing the circular (muscles 

 shows no response except to mechanical stretching while 

 the portion containing the myenteric plexus and the longi- 

 tudinal muscles will still exhibit spontaneous rhythmic 

 movements. It, therefore, seems probable that the move- 

 ments of the small intestine depend largely upon the 

 myenteric plexus and that this plexus represents a nerve- 

 net that acts on the adjacent musculature much as the 

 nerve-nets in the lower animals do. In this way the small 

 intestine, though under the influence of extrinsic nerves, 

 also retains a relatively high degree of autonomy depen- 

 dent upon its nerve-net. Its activities, particularly its 

 rhythmic segmentation, affords an excellent example of 

 von Uexkiill's principle, for the segment of the intestine 

 that is momentarily distended, whereby its nerve-net is 

 stretched, is the region into which the impulses for re- 

 newed contraction flow most freely. 

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