LECTURE XII 

 PHYSIOLOGY OF DIGESTION 



Definition. — Digestion is a chemical and physical process by 

 which food matters are made soluble and capable of absorption. 



The digestive fluids are saliva, gastric juice, pancreatic juice, 

 bile and intestinal juice. These are the active agents which 

 bring about the changes necessary to render food matters soluble 

 and absorbable. 



Food groups. — These are of two general classes : organic and 

 inorganic. 



The organic group is divided into three subgroups: carbohy- 

 drates (sugars and starches) ; proteids (egg albumin, casein, 

 gluten, etc.) ; and fats. 



The inorganic group includes water, sodium, potassium, lime, 

 sulphur, phosphorus, iron, etc. These form a very important 

 part of the ration. Normal growth of young animals is impos- 

 sible without the necessary mineral matters, especially phos- 

 phate of lime, which forms about four fifths of the total. In 

 case of older animals a mineral-deficient diet results in a mineral 

 drain from the tissues, for example in case of a cow giving milk 

 or carrying a calf. 



Course and History of Food Groups 



Carbohydrates. — Starch cells are broken up by the teeth, and 

 the starch is changed by the saliva 1 and pancreatic juice into 

 soluble sugars. Physiologists differ somewhat as to details, but 

 during the process of digestion at least two sugars,— dextrose 

 (grape sugar), maltose and dextrine, an intermediate body be- 

 tween sugar and starch, are formed. After these chemical 

 changes come absorption, storage in the liver, then distribution, 

 and use. A large part of the products are taken into the portal 



1 Authorities differ. Some deny the power of herbivorous saliva to do 

 this. 



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