IQ8 ELEMENTS OF PHYSIOLOGY 



348. Outline of Digestion. The food is made soluble in 

 the alimentary canal and is absorbed by the blood vessels 

 and lymphatics in its walls. This canal is about thirty feet 

 long (Plate III) and consists of 



(1) The mouth, where the food remains about a minute, 

 while it is chewed and mixed with the saliva ; the saliva 

 changes a portion of the starch to malt sugar. 



(2) The gullet, a tube nine inches long, running from 

 mouth to stomach and lying just in front of the vertebral 

 column. 



(3) The stomach, a large pouch where the food is stored 

 and from which it passes in the course of several hours, 

 having become semi-liquid, and the proteids having been 

 partly digested by the gastric juice, an acid secretion from 

 small glands in the stomach walls. 



(4) The small intestine, a narrow tube more than twenty 

 feet long, where the fats are acted upon for the first time, 

 and where the starches and proteids are also acted upon, and 

 where, after about ten hours, the digestion and absorption of 

 the three classes of foods is completed (Figs. 175, 177). 



(5) The large intestine, about five feet long, where the 

 last remnant of nutriment is absorbed and the indigestible 

 materials in the food are gathered together (Plate IV). 



349. Water and salt require no digestion preliminary to 

 absorption. After the food is digested and absorbed and 

 carried to the tissues by the blood and lymphatics, it must 

 be assimilated, or made into material similar to the contents 

 of the cells, and stored up for future use. Drugs, narcotics, 

 and alcohol are not stored up in the cells, but, it is believed, 

 are largely oxidized in the blood and lymph, or expelled 

 from the system unchanged. 



350. The Waste of the Body. When the foods are oxi- 

 dized in the body, there are several products of oxidation 

 called waste products. The starches and sugar, fats and 

 oils, when oxidized, give rise to water and carbon dioxid. 



