INTESTINAL NERVE MECHANISM. 



131 



rior of Meissner ; the meshes of which are looser and more 

 irregular, and the chords and ganglia more rounded and finer 

 than those of Auerbach's plexus. (Figs. 58, 59.) 



The blood flowing through these nerve centres in all probability 

 acts as a sufficient stimulus under ordinary circumstances, to pro- 

 duce some peristaltic motions, and hence we may say that they 

 are automatic. When food comes into the intestine it increases 

 the flow of blood, as well as mechanically irritating the intestinal 

 wall. The intestinal vessels remain engorged so long as the pro- 

 cess of digestion goes on. Food seems to act more effectually 



FIG. 57. 



FIG. 56. 





FIG. 56. Auerbach's plexus from between the muscle coats of the intestine, with low 

 power. 



FIG. 57. A nodal point of Auerbach's plexus under high power, showing the nerve 

 cells. 



than insoluble mechanical stimuli, for when insoluble substances 

 are placed in the gut, they at first call forth active movements ; 

 but these do not last long, for the stimulus is not of itself ade- 

 quate to excite prolonged action, except it be associated with 

 continuing congestion dependent upon other causes, such as the 

 vasomotor changes accompanying the general digestive process, 

 and the absorption of the prepared food stuffs. 



With regard to the influence of other nerves, it seems to be 

 admitted on all sides that the vagus acts as an exciting nerve, 

 since stimulation of its peripheral part causes increased action, 



