CONTROL OF GASTRIC SPHINCTERS 417 



contracted, i.e. during the iu)rnial state ol' tonus, tliese sphincters 

 prevent the too hurried passage of material along the alimentary 

 canal and also prevent its regurgitation. They are not controlled 

 by the will but by local nerve centres. By its weight, the bolus 

 usually exerts sufficient pressure to cause the opening of the 

 cardiac sphincter and gain admission to the stomach, in which 

 it is locked by the operation of a local automatic arrangement. 



The processes of digestion or splitting of the foodstnlTs by 

 enzymes now^ commence (Chap. X.). Polysaccharides are broken 

 down to maltose by ptyalin and the native proteins first converted 

 to mctaprotein by the action of the hydrochloric acid of the 

 gastric juice and reduced in size and complexity to the proteose 

 stage by the action of pepsin. 



Pre-pyloric Sphincter. 



Even a casual examination of the stomach will show that it 

 is divided into two parts, each w^ith a distinct function. Wepfer 

 (1679), Spallanzani, Haller and others observed that a transverse 

 band of muscle formed a " potential " sphincter to the antrum 

 pylori in various animals including man. " This band," writes 

 Beaumont, the obser^'er in the now classical St. Martin experi- 

 ments, " is situated near the commencement of the more conically 

 shaped part of the pyloric extremity, 3 or 4 in. from the smaller 

 end. In attempting to pass a long glass thermometer tube through 

 the aperture into the pyloric portion of the stomach, during the 

 latter stages of digestion, a forcible contraction is first perceived 

 at this point and the bulb is stopped. In a short time there is a 

 gentle relaxation, w^hen the bulb passes without difficulty and 

 appears to be drawn quite forcibly for three or four inches toAvards 

 the pyloric end. It is then released and forced back, or suffered 

 to rise again ; at the same time giving to the bulb-tube a circular 

 or rather spiral motion and frequently revolving it completely 

 over." Other observers, using more modern methods involving 

 bismuth feeding, etc., have confirmed these older findings, and 

 have shown definitely that this constriction takes place during 

 normal digestion in man, dividing the stomach into an upper, 

 fundie part, which may be completely separated physically and 

 functionally from the lower, antrum pylori. The upper or cardiac 

 portion is a reservoir or hopper where the food pulp is stored 

 for a short time without mixing. It is during its stay here that 

 salivary digestion reaches its maximum. By the steady pressure 

 of the walls in the eardia, the nnishy mass is fed little by little 

 through the throat of the hopper (prepyloric sphincter) into the 

 lower or pyloric part of the stomach. By peristaltic contractions 



