A STUDY OF BLOOD 



12. ABSORPTION FROM THE ALIMENTARY CANAL 



Necessity for Absorption. We have now learned some- 

 thing of the processes of digestion. We have seen that the 

 foods we eat are ground up in the mouth cavity by the teeth, 

 and thus made ready for the action of the various digestive 

 juices. We have also demonstrated that sugars and soluble 

 salts are dissolved in the mouth ; that insoluble mineral 

 matters are made soluble in the stomach; that starch is 

 changed to sugar by the saliva and pancreatic juice ; that 

 proteids are converted into peptones by the pancreatic and 

 gastric juices ; and that fats are emulsified or saponified 

 in the intestines by the combined action of bile and pan- 

 creatic juice. Were the food to remain within the alimentary 

 canal, however, even though it had been thoroughly digested, 

 it would still be, in a certain sense, outside the body, since 

 this canal is a continuous tube opening to the exterior at 

 either end. In order to furnish material for building and 

 repairing the various tissues, the liquid nutrients must be 

 distributed to the tissues, wherever needed. This is accom- 

 plished through the agency of the blood system. We have 

 now to consider the process of absorption, which includes the 

 final steps whereby foods become a part of blood. By absorp- 

 tion is meant the passage of the digested food through the lining 

 of the alimentary canal, and through the thin walls of the count- 

 less blood vessels and lacteals that lie close at hand. To under- 

 stand this process we must first consider 



The Principles of Osmosis. 1 An apparatus for the demon- 

 stration of osmosis is shown in Fig. 37. Over the larger end 

 of a thistle tube is tied a piece of the intestine of a sheep 

 or pig. The tube is half filled with a thick solution of grape 

 sugar (honey will do as well), and is inserted in a bottle filled 

 with water to the level of the grape sugar. The height of 

 the thistle tube is increased by attaching a glass tube. At 

 the beginning of the experiment we have two liquids (water 



1 See "Laboratory Exercises," No. 23. 



