AUEKBACH AND MEISSNER'S PLEXUSES. 



237 



[Structure. Auerbach's Plexus consists of non-medullated nerve-fibres which form a dense 

 network, groups of ganglion cells occurring at the nodes (fig. 175, and when seen in vertical 

 sections between the muscular coats it is like fig. 174). A similar plexus extends throughout 

 the whole intestine between the longitudinal and circular muscular coats from the oesophagus 

 to the rectum. Branches are given off to the muscular bundles. A similar, but not so rich a 

 plexus lies in the submucous coat, 

 Meissner's plexus, which gives branches 

 to supply the muscularis mucosae, the 

 smooth muscular fibres of the villi, and 

 the glands of the intestine (fig. 176). 



1. If this centre is not affected 

 by any stimulus, the movements of 

 the intestine cease comparable to 

 the condition of the medulla ob- 

 longata in apnoea. The same is 

 true just as in the case of the 

 respiration during intra-uterine 

 life, in consequence of the foetal 

 blood being well supplied with O. 

 This condition may be termed 

 aperistalsis. It also occurs during 

 sleep, perhaps on account of the 

 greater amount of O in the blood 

 during that state. 



2. When blood containing the 

 normal amount of blood-gases 

 passes through the intestinal blood- 

 vessels, the quiet peristaltic move- 

 ments of health occur (euperistal- 

 sis) provided no other stimulus be 

 applied to the intestine. 



3. All stimuli applied to the 

 plexus myentericus increase the 

 peristalsis, which may become so 

 very violent as to cause evacuation 

 of the contents of the large gut, 

 and may even produce spasmodic 

 contraction of the musculature of 

 dysperistalsis, corresponding to dyspnoea. The 

 through the intestinal vessels affects the peristalsis. 



Condition of the Blood. Dysperistalsis may be produced by (a) interrupting the circulation 

 of the blood in the intestines, no matter whether anaemia (as after compressing the aorta 

 Schiff) or venous hyperseinia be produced. The stimulating condition is the want of 0, i. e. , 

 the increase of C0 2 . Very slight disturbance in the intestinal blood-vessels, e.g., venous con- 

 gestion after copious transfusion into the veins, whereby the abdominal and portal veins become 

 congested, causes increased peristalsis. The intestines become nodulated at one part and narrow 

 at another, and involuntary evacuation of the fasces takes place when there is congestion, owing 

 to the plugging of the intestinal blood-vessels when blood from another species of animal is used 

 for transfusion ( 102). The marked peristalsis which occurs on the approach of death is 

 undoubtedly due to the derangements of the circulation, and the consequent alteration of the 

 amount of gases in the blood of the intestine. The sanfe is true of the increased movements of 

 the intestines which occur as a result of psychical excitement, e.g., grief. The stimulus, in this 

 case, passes from the cerebrum through the medulla oblongata (vaso-motor centre) to the intes- 

 tinal nerves, and causes anaemia of the intestine (corresponding to the palor occurring elsewhere). 

 When the normal condition of the circulation is restored, the peristalsis diminishes, (b) Direct 

 stimulation of the intestine, conducted to the plexus myentericus, causes dysperistalsis ; direct 

 exposure of the intestines to the air (stronger when C0 2 or CI is present) introduction of 

 various irritating substances into the intestine increased filling of the intestine when there is 

 any difficulty in emptying the gut (often in man) direct stimulation of various kinds (also 



Fig. 176. 

 Plexus of Meissner. a, ganglia ; b, anastomosing 

 fibres ; c, artery ; d, vaso-motor nerve-fibres accom- 

 panying c. 



the intestine. This condition may be termed 

 condition of the blood flowing 



