Condition in which Fats are absorbed from the Intestine. 441 



pletely acid to phenolphthalein, showing that the acid reaction to litmus 

 in the upper part is due to weak organic acids, while the alkaline reaction 

 in the lower is due to fixed alkali, accompanied by dissolved carbonic 

 acid. The alkaline reaction to methyl-orange in the upper part, where 

 it is acid to litmus and phenolphthalein, shows that in that part there 

 is an excess of bases, above that quantity necessary to combine with all 

 the inorganic acids, which are combined with very weak organic acids 

 (probably fatty acids), for methyl-orange is a stable indicator, and 

 does not react to such acids, while litmus, and, still more so, phenol- 

 phthalein, are indicators which are affected by these acids. In the 

 lower third or thereabouts, where the reaction is alkaline to litmus, 

 there cannot be any fatty acids present in solution. 



Any fat absorbed as free fatty acid in solution must, therefore, be 

 taken up from the upper two-thirds or three-fourths of the intestine 

 where the reaction is acid to litmus, but even here a considerable part 

 is probably being absorbed in solution as soaps, as is shown by the 

 reaction being at the same time alkaline to methyl-orange. In the 

 lower part all the fat absorbed must be taken up as soaps. 



During fat absorption in the white rat,* the reaction of the con- 

 tents of the small intestine is commonly alkaline to litmus from 

 pylorus to ceecum, and is never acid for a greater distance than 2 or 

 3 in. below the pylorus ; in this animal, therefore, nearly all the fat 

 must be absorbed in solution as soaps. 



We have not investigated the reaction of the intestinal contents 

 in other animals during fat absorption, but in the rabbit, during 

 carbohydrate absorption, it is strongly alkaline all the way, from 

 pylorus to caecum, and in the pig the mixed contents during the 

 absorption of a mixed meal (meal and oats) had a strong alkaline 

 reaction. As already stated, the filtered consents in these animals do 

 not perfectly dissolve fat, and the portion dissolved must be in the 

 form of soap, because the reaction remains, alkaline to litmus after 

 solution. In such animals it is probable that the greater part of 

 the fat must be absorbed as soaps. 



The main objections which have been urged, against absorption of 

 fats as soaps are, first, absorption in presence of an acid reaction in 

 the dog, in which case it was supposed impossible that soaps could 

 be present simultaneously in solution,f and, secondly, that the 



* In this animal the intestinal contents are usually semi-solid. Care was taken 

 to mix them so as not to obtain the alkaline surface reaction sometimes described. 

 On thorough mixing an alkaline reaction was obtaine.d. 



f The acid reaction is also commonly supposed to preclude the possibility of the 

 formation of an emulsion, and Cash ('Arch. f. Anat. u. Physiol.,' 1881, p. 386), in 

 experiments chiefly made to determine this point, failed to find any emulsion within 

 the dog's intestine. In ten out of sixteen experiments we obtained more or less 

 emulsion, and in fire of these, in almost the entire length, a perfect emulsion, con- 

 taining immense numbers of minutest fat globules, and possessing a marked acid 



2 L 2 



