CHAPTER XLIX 

 THE MECHANICAL FACTORS OF DIGESTION 



THE mechanical factor plays an important part in the processes 

 of digestion, and is intimately related with the chemical factors. The 

 mechanical factor insures the proper subdivision and mixing of the 

 food with the digestive secretions, exposes the products of digestion 

 to the absorptive surfaces, propels them from one region of the gut 

 to another, and finally discharges the waste material from the body. 

 It is obvious that these processes must be conducted in an orderly 

 fashion, otherwise the food might either be inadequately digested or 



FIG. 199. OUTLINES OF AN ALMOST INSTANTANEOUS RADIOGRAPH OF THE STOMACH 

 OF A CAT DUKING DIGESTION. (Cannon.) 



0/Cardia; P, pylorus; at 1, 2, 3, 4, 5, are indentations due to peristaltic waves 

 passing towards the pylorus. 



inadequately absorbed. The kind and rate of movement in the different 

 parts of the alimentary tract varies, therefore, according to the special 

 digestive actions which are being effected in those parts. 



The muscles at the beginning and at the end of the alimentary 

 tract are under voluntary control; the rest of the musculature of the 

 tract, however, is of the smooth variety, automatic in action. The 

 automaticity is dependent, for the most part, upon the primitive 

 nerve plexus (Auerbach's) in the wall of the gut; it is influenced by 



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