PASSAGE OF THE FAT TO THE LACTEALS. 457 



If a rabbit be killed some hours after a meal of oats, a certain amount of fat is 

 shown to be in process of absorption by the whiteness of the lacteals, but the 

 reaction of the contents of the small intestine is always markedly alkaline. 



It is probable, then, that in all animals a great part of the fat is 

 absorbed 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. 



These various theories as to the form in which fats enter the epithelial 

 cell, may be summarised as follows : 



Emulsion theories. 1. A small percentage of the fat is split up into 

 fatty acids and glycerin, the fatty acids unite with the alkaline basis of the 

 mixed secretions present in the intestine, and the rest of the fat is thereby 

 converted into an emulsion, which is absorbed by the columnar cells. 



2. A considerable part of the fat is split up into fatty acids and glycerin, 

 and absorbed as emulsified fatty acids and glycerin, which are synthesised 

 to neutral fats by the columnar cells. 



Solution theories. 1. All the fat is split up into fatty acids and glycerin ; 

 the fatty acids combine with alkaline bases to form soluble soaps ; these and 

 the dissolved glycerin are absorbed in solution, and synthesised to neutral 

 fats in the columnar cells. 



2. All the fat is split up into fatty acids and glycerin ; the fatty acids 

 are dissolved as such by the intestinal fluid (the bile being that constituent 

 which gives this solvent property to the fluid), these dissolved fractions of the 

 fat are absorbed by the columnar cells, and by these are synthesised again to 

 neutral fats. 



3. The processes indicated under solution theories 2 and 3 probably 

 mutually replace each other to a variable extent in some animals, but in 

 others absorption takes place entirely in the form of soaps. 



Passage of the fat from the epithelial cells to the lacteals. 

 In whatever form the fat passes into the columnar cells, it is certain 

 that it is here converted again into fat. During active fat absorption 

 these cells become gorged with fat globules of varying dimensions. It 

 is agreed by all observers that this fat passes from the epithelium to 

 the lacteals in the form of an emulsion, but there is some difference of 

 opinion as to the fashion in which it is conveyed. 



It has already been stated that the tissue of the villi, especially 

 during active fat absorption, contains immense numbers of leucocytes. 

 These are found not only in the subepithelial tissue, but between the 

 epithelial cells. The number in this position is greatly increased during 

 absorption, and at this time lymphoid cells occur also in the lacteals, 

 but "are found more numerously in the lacteals of the villi than in 

 those which are more deeply seated, and, most numerously of all, near 

 the blind end of the lacteal. That they pass into this vessel from 

 the surrounding lymphoid tissue is certain, for a lymphoid cell may 

 often be seen, fixed by the reagent employed for hardening the tissue, 

 in the act of passing through the wall of the lacteal." 1 After a meal 

 containing fat, these lymphoid corpuscles contain granules, which stain 

 black with osmic acid ; many of these are soluble in ether, so that they 

 are unquestionably composed of fat. 



1 Schafer, Internal. Monatschr. f. Anat. u. HistoL, Leipzig, 1885, Bd. ii. S. 6. The 

 greater part of the description of the carriage of fat by leucocytes, between epithelium and 

 lacteal, given in the text, is abstracted from this source. 



