DIGESTION AND ABSORPTION 179 



thus converted into soluble and diffusible forms, and is in a 

 condition ready for absorption through the digestive tract into 

 the circulation. It must not be concluded, however, that no 

 absorption of the products of protein digestion takes place until 

 the intestinal juice has acted upon the food mass. As will be 

 shown later when the absorption of the products of digestion 

 is considered, this process is a gradual and continual one almost 

 from the beginning of the digestive action. 



DIGESTION OF FATS 



We now come to the consideration of the digestion of the 

 third of the three essential food constituents, viz. fats. 



Fat food consists of both animal and vegetable fats and oils 

 which may be treated as one in connection with the processes 

 of digestion. The difference between the different fats and 

 oils consists in different physical properties, or different forms 

 in which they may be present in the food, e.g. as free globules 

 \ of fat, or in the form of an emulsion as in milk. The difference 

 in chemical composition of the fats and oils used as food con- 

 sists in the different fatty acids which are present in combina- 

 tion. It will be recalled that fats and oils are esters or ethereal 

 salts of glycerol and a certain few of the fatty acids, especially 

 butyric, caproic, lauric, myristic, palmitic, stearic of the satu- 

 rated series, and the unsaturated acid oleic and sometimes 

 linoHc. The metabolism of fats is somewhat dependent upon 

 the character of the fatty acid present, but the process of 

 digestion is the same for all. 



Hydrolysis of Fats. — The digestion of fats consists, chemi- 

 cally, simply in the hydrolysis of the glycerol ester into glycerol 

 and the fatty acid as represented by the following equation : 



CH2OOCC15H31 CH2OH 



CHOOCC15H31 -h 3 H2O -> CHOH -h 3 C15H31COOH 



CH2OOCC15H31 CH2OH 



Glyceryl tri-palmitate Glycerol Palmitic acid 



