290 DIGESTION 



fibers for the first part of the large intestine. The other parts and the rectum 

 are supplied by the lumbar and the sacral nerves. The former arise from the 

 second to the fourth lumbar roots, pass through the sympathetic to the inferior 

 mesenteric ganglion and so to the intestine. The sacral nerves arising from the 

 II-IV sacral roots traverse the so-called nervi errigentes (Langley, cf. page 233). 

 [According to Elliott the large intestine also receives inhibitory fibers from 

 the sympathetic. ED.] 



FOURTH SECTION 



DIGESTION IN THE DIFFERENT DIVISIONS OF THE 

 ALIMENTARY CANAL 



Now that we have become acquainted with the properties of the different 

 digestive fluids, and the processes by which they are formed, as well as with 

 the movements of the alimentary canal, there remains yet for us to consider 

 the digestive process itself in the different divisions of the canal, and to study 

 the relative importance of each division. 



By way of general remark it must be emphasized here once more that 

 appetite is of great and deep-seated importance for the entire activity of the 

 digestive apparatus. Only under its influence does a plentiful secretion of 

 gastric juice take place immediately after the ingestion of food. The acid 

 of the gastric juice in turn rouses the secretion of the pancreas which then 

 without delay pours its secretion into the intestine; when, after a longer or 

 shorter time, the stomach is emptied, the intestine is immediately prepared 

 to continue the work of digestion and to carry it forward to the end. 



Our knowledge of the conditions which control the movements of the 

 alimentary canal are still too meager to permit us to say anything as to the 

 importance of appetite and of eating for them. Certain observations of 

 Pawlow show that desire for food does exert an actual influence on the move- 

 ments of the stomach. Thus spontaneous movements of this organ are sup- 

 pressed when the animal is greatly excited by the sight of food : the stomach 

 is preparing itself for the reception of food (cf. also note, page 284). 



1. DIGESTION IN THE MOUTH 



The most important function of the mouth with reference to digestion 

 is the mechanical reduction of the food, and the admixture of saliva with it. 

 Substances soluble in water are dissolved by the saliva and, what is more 

 important," the morsel of food is rendered slippery by the mucin therein 

 contained, and thus is the more easily passed through the gullet to the stomach. 



The latter function is confirmed by the following observation of Cl. Bernard. 

 An oesophageal fistula was made in the neck of a horse and the animal was given 

 mouthfuls of wet oats. In one minute there came through the opening of the 

 fistula 55 g. of the oats. After the ducts of the two parotid glands were cut off 

 so as to shut out the saliva from the mouth, only 14.4 g. came through in one 

 minute. The mucus secreted by the glands of the pharynx and oesophagus also 

 aids the passage of the bolus. 



