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or 



ABSORPTION OF FAT. 263 



-v- 



Solution Theories. Of these there are two : (1) the soap theory 

 and (2) the fatty-acid theory. 



Soap Theory. This theory takes cognizance of the fact that 

 soaps are formed in the small intestine by the action of steapsin 

 on the neutral fats, by which they are split up into fatty acids 

 and glycerin, the fatty acids uniting with some of the alkali of 

 the intestinal fluids/ with the result of forming soluble alkaline 

 soaps. The theory' under consideration supposes that these soaps, 

 together with the glycerin, are absorbed by the columnar epithe- 

 lium, and that when within the protoplasm the acids and glycerin 

 again unite by virtue of cell-action to form neutral fat, which is 

 seen in the interior of the cells. We have already referred to the 

 fact that pancreatic juice has the power of decomposing all the 

 fat of an ordinary meal into fatty acids and glycerin during the 

 time that it remains in the small intestine. The objection to the 

 soap theory, that there is not enough alkali in the body to com- 

 bine with the fatty acids which would result from the decomposi- 

 tion of the fat which is taken in as food, is met by the explanation 

 that only a small amount is needed at a given time to form a soap, 

 and that as soon as the soap has entered the cells it is again decom- 

 posed into fatty acids and alkali, the latter returning to the blood 

 and being again available for use, while the acids unite with the 

 glycerin to form neutral fat. 



'Fatty Acid Theory. The other theory is that fatty acids, formed 

 in the manner stated, are dissolved by the bile, and in this form 

 are absorbed, the fatty acids uniting with the glycerin which was 

 absorbed at the same time and forming neutral fat. There is 

 evidence showing that when fatty acids alone are absorbed, glycerin 

 is formed, probably by the columnar epithelium, and that by the 

 union of the two neutral fat is produced. 



The evidence seems conclusive that fats are absorbed as soaps 

 and fatty acids, and not as emulsified fat, the fatty acids being 

 dissolved by the bile, the salts and pseudomucin of which are the 

 efficient factors in causing this solution. 



In summing up this portion of the section on the a Chemistry 

 of the Digestive Processes," in Schafer's Text-Book of Physiology, 

 Moore says : "It is probable, then, that in all animals a great 

 part of the fat is absorbed and dissolved in the form of soaps ; 

 but in some animals a part is also absorbed as dissolved fatty 

 acids, while in others the entire quantity leaves the intestine in 

 the form of soaps." 



Course of Fat from Columnar Epithelium to the Lacteals. 

 Although fat is not absorbed as an emulsion, it is in this form that 

 it exists in the interior of the epithelial cells after its re-formation 

 from the fatty acids and glycerin. We have already referred to 

 the large number of lymph-corpuscles, or leukocytes, in the tissues 

 composing the villi. During the absorption of fat these cells 

 contain fat, and they doubtless carry this to the lacteals, there 



