3 66 



FOOD AND DIGESTION 



maintain the nervous relations intact, and it led to secretion of gastric juice 

 in the main part of the stomach. This is undoubtedly a nervous reflex effect. 

 Recently observations on a case of stricture of the human esophagus 

 which prevented food from reaching the stomach have shown that an 

 abundant flow of gastric juice takes place when food is taken into the mouth. 



RV 



FIG. 259. Very Diagrammatic Representation of the Nerves of the Alimentary 

 Canal. Oe to Ret, the various parts of the alimentary canal from esophagus to rectum; 

 L. V, left vagus, ending on front of stomach; rl, recurrent laryngeal nerve, supplying upper 

 part of esophagus; R. V, right vagus, joining left vagus in esophageal plexus; as. pi., 

 supplying the posterior part of stomach, and continues as R' V to join the solar plexus, here 

 represented by a single ganglion, and connected with the inferior mesenteric ganglion, m. 

 gl.; a, branches from the solar plexus to stomach and small intestine, and from the mesen- 

 teric ganglia to the large intestine; Spl. maj., large splanchnic nerve, arising from the 

 thoracic ganglia and rami communicantes; r. c., belonging to dorsal nerves from the 6th 

 to the Qth (or loth); Spl. min., small splanchnic nerve similarly from the loth and nth 

 dorsal nerves. These both join the solar plexus, and thence make their way to the ali- 

 mentary canal; c. r., nerves from the ganglia, etc., belonging to nth and i2th dorsal and 

 ist and 2d lumbar nerves, proceeding to the inferior mesenteric ganglia (or plexus), m. gl., 

 and thence by the hypogastric nerve, n. hyp., and the hypogastric nerve, n. hyp., and the 

 hypogastric plexus, pi. hyp., to the circular muscles of the rectum; /. r., nerves from the 2d 

 and 3d sacral nerves, S. 2, S. 3 (nervi erigentes) proceeding by the hypogastric plexus to the 

 longitudinal muscles of the rectum. (M. Foster.) 



It seems conclusively established at the present time that the secretion of 

 gastric juice is a reflex act controlled by a definite nervous mechanism. This 

 reflex can be aroused by the sensory stimuli of taste, smell, and even sight. 

 It can also be initiated by stimuli arising in the stomach itself by the effects 

 of ingredients of the food or by the products of digestion. Indeed, it has 

 been shown that peptone is a very efficient stimulus for this stomach reflex. 



Edkins, however, has recently shown that the contact of certain food 

 products with the pyloric end of the stomach, where they are slightly ab- 

 sorbed, gives rise to some chemical substance a gastric hormone or secre- 



