700 



PHYSIOLOGY 



that the pylorus remains firmly closed so long as the contents of the duo- 

 denum are acid. If alkaline fluid be introduced into the stomach, this is 

 rapidly passed into the duodenum. If, however, some acid be introduced at 

 the same time into the duodenum by means of a duodenal fistula, the pylorus 

 remains firmly closed, and no fluid passes into the duodenum until the acid 



LSyiCh 



FIG. 339. Distribution of the vagus in the abdomen of the dog. 



(M. H. NAYLOR.) 



RV, LV, right and left vagi. The right vagus runs behind the oesophagus 

 (Oe) and stomach (St), and in those places is represented by a discontinuous 

 line. Cb, connecting branch between right and left vagi ; P, pancreas ; Dd, 

 duodenum ; FD J, flexura duodeno-jejunalis ; I, I, I, intestine ; L, liver ; 

 K, kidney ; A, suprarenal capsule ; RG, LG, right and left cura of diaphragm ; 

 L.Sy.Ch, left sympathetic chain ; 12 D, 13 D, twelfth and thirteenth dorsal 

 ganglia ; 3 L, third lumbar ganglion ; G.Sp.N, L.Sp.N, great and small 

 splanchnic nerves ; S.G, left semilunar and superior mesenteric ganglia ; 

 D.A, dorsal aorta. 



which was placed there has been neutralised by the secretion of pancreatic 

 juice and succus entericus. We have probably in the walls of the alimentary 

 canal a local nervous mechanism for the movements of the pyloric sphincter. 

 This may be played upon by impulses starting either in the stomach or in 

 the duodenum, probably by the contact of acid with the mucous membrane. 

 Increasing acidity on the side of the stomach causes relaxation of the orifice, 

 whereas acidity on the duodenal side causes contraction of the pyloric 



