462 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



sion at all, or only absorb it at a greatly diminished rate. 1 There is no 

 experimental evidence in support of this theory, and a great objection to 

 it is that bile is constantly present in the intestine, and is not poured 

 out in association with the presence of fat ; such are not the proper 

 conditions for a stimulus, which ought, if it is to be effective, to be inter- 

 mittent, and only be called into action when required. 



6. All the previous views rest on the assumption that the fats are 

 absorbed in the form of an emulsion. If, on the other hand, the fats are 

 absorbed in soluble forms as fatty acids or soaps and glycerin, the most 

 obvious explanation of the action of bile and pancreatic juice in assisting 

 absorption is, that these secretions increase the solubility of the fatty 

 acids or soaps. 



In the absence of bile or pancreatic juice, the fatty acids are not so 

 soluble in the intestinal fluid, and so tfie absorption is defective, and the 

 insoluble fatty acids appear in the faeces. In support of this the fact 

 may be recalled that the bile salts possess the power of dissolving the 

 insoluble soaps of the alkaline earths. 2 



Channels of absorption of the fats. There is no doubt that the 

 lacteals are the main channel by which the fats are carried away from 

 the intestine, but it is by no means so clear that all the fat goes by this 

 route. The amount of fat absorbed from the intestine after a fatty meal 

 can easily be determined by weighing the amount of fat ingested, and that 

 remaining in the alimentary canal when digestion is nearly complete, and 

 taking the difference, which must be the amount absorbed. The amount 

 of fat poured into the blood by the thoracic duct during the same period 

 can also be determined, by inserting a cannula into the duct and collecting 

 the chyle, from which the fat is afterwards extracted and then weighed. 

 The amount thus carried by the thoracic duct during the period of active 

 absorption is always much less than the total quantity absorbed ; it lias 

 never been found to amount to more than 60 per cent., and is usually 

 much less than this. 3 The fate of the balance of the fat is unknown ; the 

 first suggestion occurring to the mind, that it travels by the alternate 

 path of the portal circulation, has not been found to fit the experimental 

 facts. The portal vein during fat digestion does indeed contain an 

 abnormal amount of finely emulsified fat, but so does all the blood of the 

 body, and the presence of the fat is due to the admixture with the blood 

 of the chyle carried by the thoracic duct. On diverting from the blood 

 this supply of fat, by means of a cannula inserted into the thoracic duct, 

 Zawilski found scarcely any fat in the blood during fat absorption. 

 Neither is there any difference during fat absorption in the percentages 

 of fat present in portal and carotid blood. 4 It would seem from this 

 that almost all the fat is carried by the lacteals, but that part is 

 removed somewhere in the lymphatic system between the lacteals and 

 the opening of the thoracic duct ; it may be in the lymphatic glands, 5 

 but the subject requires further investigation. 



1 Rohmann, Arch. f. d. ges. Physiol., Bonn, Bd. xxix. S. 509 ; Minkowski, BerL med. 

 Wchnschr., 1890, No. 15, S. 333 ; Lewin, Arch. f. d. ges. Physiol. , Bonn, 1896, Bd. Ixiii. 

 S. 186. 



2 See p. 392. 



3 Zawilski, Arb. a. d. physiol. Anst. zu Leipzig, 1867, Bd. xi. S. 147 ; "\Valther, Arch, 

 f. Anat. u. PhysioL, Leipzig, 1890, S. 329; Frank, ibid., 1892, S. 497 ; Munk u. Rosen- 

 'stein, Virchow's Archiv, Bd. cxxiii. S. 484. 



4 Heidenhain, Arch. f. d. ges. PhysioL, Bonn, 1888, Bd. xliii., Supp. Heft, S. 95. 



5 See M. Foster, "Text-book of Physiology, " pt. ii. p. 513. 



