THE ALIMENTARY CANAL 187 



tion or any similar treatment of food is that subdivision 

 increases the surface exposed to the juices. This is 

 just as true when an oil is broken into fine drops 

 emulsified as when we have to do with solids. 



Much that has gone before can be made clearer by 

 considering what kinds of food need no digestion. This 

 is the case with the simple sugars, the dextrose of grapes 

 and honey, the levulose in many fruits. It is also true 

 of the various mineral salts of the diet, so far as they are 

 destined to be absorbed, and of alcohol. Any other kind 

 of food can, theoretically, be predigested, but the ad- 

 vanced cleavage products in the case of proteins and 

 fats are not appetizing. 





