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 the 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 absorl >ed ; it has 
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. gcs. Physiol., Bonn, Bd. xxix. S. 509 ; Minkowski, Berl. med. 
TVchnschr., 1890, No. 15, S. 333 ; Lewin, Arch. f. d. gcs. Physiol., Bonn, 1896, Bd. lxiii. 
S. 186. 
2 See p. 392. 
3 Zawilski, Arb. a. d. physiol. Ai>s/. :n Leipzig, 1867, Bd. xi. S. 147 ; "Waltlier. Arch. 
f. Anat. u. Physio?.. Leipzig, 1890, S. 329; Frank, ibid., 1892, S. 497; Munk u. Rosen- 
stein, Virchow's Archii; Bd. exxiii. S. 484. 
4 Heidenhain, Arch. f. d. gc*. Physiol., Bonn, 1888, Bd. xliii., Supp. Heft, S. 95. 
5 See M. Foster, "Text-book of Physiology," pt. ii. p. 513. 
