DIGESTION 133 



rendered sufficiently minute. Such a condition has been 

 almost obtained by agitating oil and water with powdered 

 glass. But the more viscous the medium through which oil 

 globules are distributed, the greater is the resistance to their 

 fusion. If oil which has become rancid in which a certain 

 quantity of fatty acid has been liberated from the glycerin 

 with which, in a neutral fat, it is combined is shaken with 

 water containing carbonate of soda, an emulsion is easily 

 formed. The carbonate of soda and the fatty acids form 

 soaps. A solution of soap is sufficiently viscous to keep the 

 droplets of oil apart. Emulsification of fats occurs in the 

 intestine. It might be assumed that the epithelial cells ingest 

 fat in this finely divided state. But it must be remembered 

 that, however minute the droplets, they are enormously large 

 as compared with the molecules of peptones and sugar which 

 the epithelial cells absorb. It is unlikely that fat is absorbed 

 in a manner so widely different from that in which other foods 

 enter the epithelial cells. Nor is it necessary to make any 

 such assumption. Pancreatic juice contains a ferment which 

 rapidly splits fats into their constituent fatty acids and glycerin. 

 In the presence of an alkali the fatty acids are converted into 

 soaps. In this soluble condition of soap and glycerin the fats 

 are probably absorbed. As soon as they have entered the 

 cellj the fatty acids and glycerin reunite 'to form" fats, setting 

 the alkali free. The alkali is returned to the intestine, where 

 it is available as a solvent of further droplets of fat. The 

 droplets of fat accumulate in the epithelial cells. During 

 active digestion they are also to be seen in the connective- 

 tissue cells, in the leucocytes, and in the lymph inside the 

 lacteal vessel. The epithelial cells extrude the oil droplets, 

 backwards, much in the same way as the cells of the mammary 

 glands extrude globules of milk. In herbivora, and in Man 

 also so far as we can judge, the contents of the small intestine 

 are alkaline. Conditions are therefore favourable for the 

 formation of soap. But in carnivora the contents are acid 

 throughout the greater part of the canal. Acid, it need hardly 

 be stated, prevents saponification. Yet carnivorous animals 

 have an immense capacity for absorbing fat. Fatty acids 

 are soluble to a moderate extent in bile. It is possible that, 

 fats having been split into fatty acids and glycerin, the 



