CHAPTER XI. 



THE DIGESTION AND ASSIMILATION OF THE 

 FOODSTUFFS. 



THE DIGESTION OF THE CARBOHYDRATES. 



The Starch in our diet is converted by cooking into "soluble starch" 

 which is much more readily hydrolyzed by the starch-splitting enzymes 

 or Amylase 1 than the uncooked material. The first enzyme to en- 

 counter the foodstuffs upon their introduction into the alimentary 

 canal is the amylase or Ptyalin of saliva. This enzyme energetically 

 hydrolyzes the starch to maltose, and it is for this reason that starch, 

 when it is held in the mouth, presently begins to taste sweet. 



There is no amylase in the Gastric Juice, but nevertheless the diges- 

 tion of starch or glycogen continues for some time in the stomach, 

 because the optimum reaction for amylase is a very faint acidity. The 

 gastric juice itself is strongly acid, in fact, far too acid to permit the 

 action of amylase if this enzyme were received directly into unneutral- 

 ised and undiluted gastric juice. But various constituents of the diet, 

 and especially the proteins, combine with the Hydrochloric Acid of the 

 gastric juice and partially neutralize it, so that the contents of the 

 stomach during the partaking of a meal and the earlier periods of 

 digestion are either neutral or only faintly acid. Long before the 

 acidity of the gastric contents approaches that of pure gastric juice, 

 the pyloric sphincter opens and permits the passage of the semi- 

 digested foodstuffs in small portions at a time into the lumen of the 

 small intestine. 



The maltose which is thus formed by the digestion of starch is not 

 normally absorbed from the stomach either as such, or in the form 

 of its further cleavage-product, glucose. Under normal conditions 

 there is little or no absorption of maltose or other sugars from the 

 stomach. If the pylorus be ligated, some absorption of sugar will 

 then be found to occur, but only under conditions involving abnormal 

 dilatation. No carbohydrate-splitting enzymes are found in the 

 gastric juice of man. It is stated that Lactase may often be found in 

 the gastric juice of the calf, but not in the adult animal. 



After the foodstuffs have remained in the stomach for a sufficiently 

 long period to allow the Chyme to become faintly acid through admix- 

 ture with an excess of gastric juice, the pyloric sphincter opens and 

 permits the passage of the chyme into the upper part of the small 



1 The amylases are frequently referred to as Diastases. In French scientific litera- 

 ture the word "Diastase" is used as a generic term to include all types of enzymes. 



