96 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



It is the fundus, and not the pylorus, which serves as a 

 reservoir and in which the greater part of gastric digestion 

 occurs. The precise condition of the pyloric sphincter dur- 

 ing gastric digestion is unknown. It may have simply an ex- 

 alted degree of tonicity which does not completely close the 

 opening and which can be overcome by pressure, or it may be 

 tightly contracted and require a distinct nervous dispensa- 

 tion to effect its relaxation for the passage of fluids as well 

 as solids. It would seem that the length of time for which 

 food is detained in the stomach depends more upon its phy- 

 sical condition than upon its chemical that is, that upon 

 any stage of digestion which it may have reached ; for it can 

 be shown that fluids pass very quickly into the intestine. 



The secretory occurrences during these movements are of 

 the greatest importance (see pp. 86-88). 



Nerve Supply. The stomach is supplied with pneumo- 

 gastric and sympathetic fibers. The latter can be traced 

 through the solar plexus, splanchnics and cervical ganglia to 

 the spinal cord. They exert an inhibitory effect on the mus- 

 cular tissues; their stimulation causes relaxation. The 

 vagus fibers are motor ; their stimulation causes contraction. 

 But these nerves serve only to regulate the muscular move- 

 ments. It is the stimulus of food in the stomach which ex- 

 cites gastric peristalsis. It is not stopped by section of the 

 nerves, though it may be interfered with. This stimulation 

 is exerted either directly upon the nerve fibers or upon the 

 ganglia of the stomach wall. 



The conditions influencing gastric digestion operate mainly 

 through changes in the quality and quantity of gastric juice. 



Digestion and Absorption in the Intestines. 

 The Small Intestine. 



Anatomy. The small intestine extends from the pylorus 

 to the caput coli, and is about twenty feet in length. It lies 

 in numerous coils which are held loosely in place by a fold of 



