DIGESTION. 375 



the large intestine it loses more water, and the digestion of 

 starch and the absorption of fats is continued. Finally the 

 residue, with some excretory matters added to it in the large 

 intestine, collects in the sigmoid flexure of the colon and in 

 the rectum, and is sent out of the Body from the latter. 



The Digestion of an Ordinary Meal. We may best sum 

 up the facts stated in this chapter by considering the diges- 

 tion of a common meal; say a breakfast consisting of bread 

 and butter, beefsteak, potatoes and milk. Many of these 

 substances contain several alimentary principles, and, since 

 these are digested in different ways and in different parts of 

 the alimentary tract, the first thing to be done is to consider 

 what are the proximate constituents of each. We thus sepa- 

 rate the materials of the breakfast as in table on next page. 



From such a meal we may first separate the elastin, cellu- 

 lose, and calcium sulphate, as indigestible and passed out of 

 the Body in the same state and in the same quantity as they 

 entered it. Then come the salines which need no special 

 digestion, and, taken either in solution or dissolved in the 

 saliva or gastric juice, are absorbed from the mouth, stomach, 

 and intestines without further change. Cane and grape 

 sugars experience the same lot, except that any cane sugar 

 or maltose reaching the intestines before absorption is 

 changed into grape sugar by the succus entericus. Calcium 

 phosphate will be dissolved by the free acid in the stomach, 

 yielding calcium chloride, which will be absorbed there or in 

 the intestine. Starch will be partially converted into maltose 

 ng mastication and deglutition, and it is possible that 



e of this sugar may be absorbed from the stomach. 



great part of the starch will, however, be passed on 

 into the intestine unchanged, since the action of saliva is 

 suspended in the stomach; and its conversion will be com- 

 pleted by the pancreatic secretion, and perhaps by the ptyalin, 

 though this is probably destroyed in the stomach by the gastric 

 juice; but in any case the starch will only have been changed 

 to maltose, and will need further digestive treatment. '-/The 

 various proteids will be partially dissolved in the stomach 

 and converted into peptone, which will in part be absorbed 

 there; the residue, with the undigested proteids, will be 

 passed on to the intestines. There the bile will precipitate 

 the peptones and parapeptones and, with the pancreatic 

 secretion, render the chyme alkaline, and so stop the activity 



