CHAPTER VIII 



FROM THE ALIMENTARY CANAL TO THE HEART 



76. Review. We have now learned what parts the 

 various digestive organs play in the preparation of foods 

 for the blood. We have seen that proteids, carbohydrates, 

 and fats are the only foods that must undergo chemical 

 changes in order to be dissolved. Water, salt, and 

 oxygen can enter the blood unchanged. We have 

 learned that the carbohydrates are changed into sugars, 

 the proteids are dissolved, and the fats and oils are 

 broken up into very small droplets and a small 

 amount is changed to soap. We have seen how the 

 oxygen gets through the walls of the air sacs of the 

 lungs, and into the plasma of the blood, where it is 

 picked up by the red corpuscles. 



We shall learn in this chapter how the peptones, 

 sugars, fats, salt, and water get through the walls of the 

 body and into the blood. You will remember that the 

 alimentary canal is a tube extending through the body, 

 and anything that is in the stomach or in the intes- 

 tines is in the alimentary canal but really not in the 

 body. The digestive tract is lined with a delicate mu- 

 cous membrane which serves as a sentinel to protect 

 the body against substances that are not dissolved and to 



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